The kW calculator
built for real electrical work

Convert kilowatts to amps, horsepower, kVA, kWh and BTU/hr across DC, single-phase and three-phase circuits, and see the actual formula, with your own numbers substituted into it, beneath every result. Built for electricians, engineers, and anyone sizing a load, a motor or a generator.

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Current type

Power (kW)

Voltage (V)

For three-phase, enter the line-to-line voltage unless you picked line-to-neutral.

Power factor (0.01 to 1.00)

Not sure? Use 1.00 for heaters and resistive loads, or 0.80 for mixed motor loads.

Current

46.30A

Formula

A = (kW × 1000) / (V × PF)

A = (10 × 1000) / (240 × 0.9) = 46.30 A

Apparent: 11.11 kVA
Reactive: 4.84 kVAR
Real: 10,000 W

Reverse check: 46.30 A converts back to 10.00 kW

Every result above is produced by the same four formulas printed throughout this page. Nothing is rounded before the final display, and the reverse check converts the answer back to confirm it.

Common kW to amps and amps to kW conversions

Every row states the voltage and power factor it assumes, so each one stands on its own without any surrounding context. Change either assumption and the number changes. The calculator above will recompute it for your exact circuit.

Kilowatts to amps

1.5 kW to amps12.5 A120 V single-phase, PF 1.00

2.2 kW to amps10.2 A240 V single-phase, PF 0.90

3 kW to amps12.5 A240 V single-phase, PF 1.00

5 kW to amps20.8 A240 V single-phase, PF 1.00

7 kW to amps29.2 A240 V single-phase, PF 1.00

7.5 kW to amps34.7 A240 V single-phase, PF 0.90

9 kW to amps37.5 A240 V single-phase, PF 1.00

10 kW to amps46.3 A240 V single-phase, PF 0.90

11 kW to amps15.9 A400 V three-phase (line-to-line), PF 1.00

15 kW to amps24.1 A400 V three-phase (line-to-line), PF 0.90

20 kW to amps26.7 A480 V three-phase (line-to-line), PF 0.90

22 kW to amps31.8 A400 V three-phase (line-to-line), PF 1.00

30 kW to amps40.1 A480 V three-phase (line-to-line), PF 0.90

50 kW to amps66.8 A480 V three-phase (line-to-line), PF 0.90

100 kW to amps133.6 A480 V three-phase (line-to-line), PF 0.90

500 kW to amps668.2 A480 V three-phase (line-to-line), PF 0.90

Amps to kilowatts

15 amps to kW1.8 kW120 V single-phase, PF 1.00

20 amps to kW4.8 kW240 V single-phase, PF 1.00

30 amps to kW7.2 kW240 V single-phase, PF 1.00

40 amps to kW9.6 kW240 V single-phase, PF 1.00

48 amps to kW11.5 kW240 V single-phase, PF 1.00

50 amps to kW12.0 kW240 V single-phase, PF 1.00

60 amps to kW14.4 kW240 V single-phase, PF 1.00

100 amps to kW24.0 kW240 V single-phase, PF 1.00

200 amps to kW48.0 kW240 V single-phase, PF 1.00

400 amps to kW299.3 kW480 V three-phase (line-to-line), PF 0.90

What is a kilowatt?

A kilowatt (kW) is one thousand watts, and a watt (W) is the rate at which one joule of energy is transferred each second. It is a measure of how fast energy moves, not how much of it has moved. A 9 kW electric shower and a 9 kW industrial heater place the same instantaneous demand on their supply, regardless of how long either one runs. Smaller quantities are expressed in milliwatts (mW) for signal-level electronics, and larger ones in megawatts (MW) for generating plant.

The unit most often confused with it is the kilowatt-hour (kWh), which measures energy rather than power: one kilowatt sustained for one hour. That distinction is why a utility bill is denominated in kWh while a circuit breaker is chosen from kW and amps. The bill charges for energy delivered over a month; the breaker responds to the rate of flow at any given instant.

The kilowatt is useful because it is the bridge unit of electrical work. Voltage alone tells you nothing about how much work a circuit does, and current alone tells you nothing without the voltage behind it. Power combines the two, and once a load is expressed in kilowatts it can be translated into almost any other unit an installation cares about: amperes (A) for conductor and breaker selection, horsepower (HP) for motor ratings, kilovolt-amperes (kVA) for transformer and generator capacity, BTU per hour or tons of refrigeration for heating and cooling, and kilowatt-hours for running cost.

What one kilowatt converts into
Convert to	Formula	1 kW equals
Amps (single-phase)	A = (kW × 1000) / (V × PF)	4.17 A at 240 V, PF 1.00
Horsepower	HP = kW / 0.7457	1.341 HP
Kilowatt-hours	kWh = kW × hours	1 kWh per hour of running
BTU per hour	BTU/hr = kW × 3412.14	3,412.14 BTU/hr
Kilovolt-amperes	kVA = kW / PF	1.25 kVA at PF 0.80
Tons of refrigeration	tons = kW / 3.516853	0.284 tons

The amperage row is the only one that needs extra information: current depends on the system voltage and, on AC, the power factor. Every other conversion in the table is a fixed ratio.

How to use this calculator

1
Choose the conversion direction
Pick kW to amps if you know a load rating in kilowatts and need the current it will draw, or amps to kW if you have a meter reading in amps and want real power. The swap button carries your result across into the opposite direction without reloading the page.
2
Select the current type
Choose DC, AC single-phase, or one of the two three-phase forms. This selection decides which formula runs: three-phase line-to-line introduces the 1.732 multiplier, line-to-neutral uses 3 instead, and DC drops the power factor term entirely.
3
Enter the system voltage
Type the voltage or tap a preset: 120 V and 240 V for North American residential circuits, 208 V and 480 V for commercial three-phase, and 400 V for European three-phase. For a three-phase calculation, enter the line-to-line voltage unless you selected the line-to-neutral option.
4
Set the power factor
Enter a power factor between 0.01 and 1.00. The field is hidden for DC because voltage and current stay in phase there. The result, the apparent and reactive power readouts, and the substituted formula all update on every keystroke.

If you don't know your power factor. Use 1.00 for purely resistive loads (electric heaters, immersion elements, incandescent lamps, ovens and toasters), because their current stays in phase with the voltage. Use 0.80 as a working estimate for mixed loads that include motors, and 0.85 for an induction motor running near full load. These are rules of thumb for planning arithmetic, not measured values: the figure printed on the equipment nameplate, or a reading taken with a clamp meter, is the one that reflects your actual circuit.

Active power, apparent power, and reactive power

On a DC circuit, power is simply voltage times current and there is only one figure to talk about. On alternating current it splits into three, because voltage and current do not necessarily peak at the same moment. When a load is purely resistive they stay in step and all the supplied power does work. When a load is inductive (any motor, transformer or ballast with a winding in it), the current lags behind the voltage, and part of each cycle is spent pushing energy into a magnetic field and then taking it back out again.

That returned energy never becomes work, but it still travels down the conductors on its way in and out. Real power (kW) is the part that does become work. Reactive power (kVAR) is the part that sloshes back and forth. Apparent power (kVA) is the total the supply has to carry to deliver both.

Quantity	Unit	What it measures	Formula
Real power (active power)	kW	The share of supplied power actually converted into work, heat or light.	P = V × I × PF
Apparent power	kVA	The total power the supply, conductors and protective devices must carry.	S = V × I
Reactive power	kVAR	Power exchanged with magnetic and electric fields without doing useful work.	Q = V × I × sin φ

kVA² = kW² + kVAR²

The three quantities form a right-angled triangle known as the power triangle, with real power along the base, reactive power up the side, and apparent power as the hypotenuse. A load drawing 10 kW at a power factor of 0.8 therefore represents 12.5 kVA of apparent power and 7.5 kVAR of reactive power. This is why conductor and protective-device selection tracks apparent power rather than real power: the wire has to carry the full 12.5 kVA worth of current even though only 10 kW of it accomplishes anything. Improving the power factor shrinks the reactive side of the triangle, which shrinks the current for the same useful output.

Single-phase power

A single-phase supply delivers alternating current through one live conductor and one return path, so the instantaneous voltage rises and falls as a single sine wave at the supply frequency: 60 Hz in North America, 50 Hz across most of the rest of the world. Nearly every home circuit and small commercial circuit is single-phase.

North American residential service is a variation called split-phase. The utility transformer supplies two hot conductors whose waveforms are 180 degrees apart, plus a grounded neutral tapped from the centre of the winding. Measuring from either hot conductor to the neutral gives 120 V for lighting and general receptacles; measuring across the two hot conductors gives 240 V for the heavy loads: the range, the dryer, the water heater, an EV charger. All the voltages quoted here are RMS values, which is what a multimeter displays and what every formula on this page expects.

Amps from kilowatts

A = (kW × 1000) / (V × PF)

Kilowatts from amps

kW = (V × A × PF) / 1000

What the diagram shows: two hot conductors, L1 and L2, and a neutral N leaving a service panel. Because L1 and L2 are 180 degrees out of phase, each measures 120 V to the neutral while the two together measure 240 V across each other. A 120 V circuit connects one hot conductor and the neutral; a 240 V circuit connects both hot conductors and may not need the neutral at all.

Three-phase power

A three-phase supply carries three separate alternating voltages of equal magnitude, each offset from the next by 120 electrical degrees. As one phase falls, another is rising, so the combined power delivered to a balanced load stays nearly constant instead of pulsing to zero twice per cycle the way single-phase power does. That steadiness is why virtually all industrial motors, large HVAC plant and commercial distribution run on three phases.

It also moves more power through less copper. Because the three phases share the return path (in a balanced three-phase load the currents cancel at the neutral point), a three-phase system transmits substantially more power than three separate single-phase circuits built from the same quantity of conductor. Lower current for the same power also means lower resistive losses in the cable.

Two wiring configurations are in common use. In a delta arrangement the three windings form a closed triangle with no neutral point, which suits motors and the primary side of distribution transformers. In a wye, also called star, one end of each winding joins at a shared neutral, making two voltages available from the same service: the higher line-to-line value (also called phase-to-phase) between any two phases, and the lower line-to-neutral value (also called phase-to-neutral) between one phase and neutral. North American commercial service is typically 480 V line-to-line (277 V to neutral) or 208 V line-to-line (120 V to neutral), while the UK, Europe and much of Asia standardise on 400 V line-to-line (230 V to neutral).

What the waveform shows: three voltages of identical magnitude and frequency traced across one complete 360-degree cycle, each one shifted 120 degrees from the next. L1 peaks first, L2 a third of a cycle later, then L3. Because the three are staggered this way, at no point in the cycle are all of them near zero together, which is why the power delivered to a balanced load stays steady rather than pulsing. The same 120-degree stagger is what makes the phase voltages add vectorially instead of arithmetically, and that vector sum is where the √3 in the line-to-line formulas comes from.

What the schematics show: on the left, three windings connected end to end in a closed triangle with the line conductors L1, L2 and L3 taken from its corners and no neutral point anywhere. On the right, the same three windings joined at a common centre point which becomes the neutral N, with the three lines radiating outward. The wye centre point is what makes a lower line-to-neutral voltage available alongside the line-to-line voltage; the delta has no such point, so only one voltage exists.

The four three-phase formulas

Which multiplier you use depends entirely on which voltage you measured. Line-to-line voltage takes √3 (approximately 1.732); line-to-neutral voltage takes 3. Both forms describe the same circuit and return the same answer, because line-to-line voltage equals √3 times line-to-neutral voltage.

Line-to-line · amps from kW

A = (kW × 1000) / (√3 × V × PF)

Line-to-line · kW from amps

kW = (√3 × V × A × PF) / 1000

Line-to-neutral · amps from kW

A = (kW × 1000) / (3 × V × PF)

Line-to-neutral · kW from amps

kW = (3 × V × A × PF) / 1000

Power factor

Power factor is the ratio of real power to apparent power: kW divided by kVA. It runs from 0 to 1 and can never exceed 1, because a load cannot convert more energy into work than the supply delivers to it. A purely resistive load sits at 1.00, often called unity power factor. An induction motor at full load typically sits near 0.85, and the same motor spinning with nothing attached can fall to 0.35, because almost all the current it draws is going into magnetising its core rather than turning anything.

Low power factor costs money in three separate ways. Current for a given real load rises as power factor falls (at 0.7 the same useful output demands roughly 43% more current than at 1.00), so conductors and protective devices must be larger. Higher current means higher resistive losses in the cable, which is energy paid for and thrown away as heat. And many commercial and industrial tariffs bill reactive demand directly or apply a surcharge below a threshold, commonly around 0.95. Facilities carrying a persistently poor power factor can install power factor correction equipment, usually capacitor banks sized to offset the inductive part of the load, which cancels some of the reactive component locally and brings both the current and any surcharge back down.

Typical power factor by load type: representative reference figures, not measured values
Load type	Typical power factor	Why it lands there
Resistive load (heater, incandescent lamp)	1.00	Voltage and current stay in phase, so every amp does useful work.
LED lighting	0.90 to 0.95	Switch-mode drivers with power-factor correction, though cheap drivers do worse.
Fluorescent lighting (electronic ballast)	0.95	Corrected ballasts hold the current close to in-phase.
Synchronous motor	0.90	Field excitation can be adjusted, so power factor is partly controllable.
Induction motor, full load	0.85	Magnetising current is small relative to the working current.
Induction motor, no load	0.35	Magnetising current dominates when there is no mechanical work being done.
Arc furnace	0.70 to 0.80	A highly variable, non-linear load with large reactive demand.

Treat these as starting estimates for planning arithmetic. Real power factor varies with load level, supply voltage and equipment age, and the nameplate figure or a clamp meter measurement is what applies to a specific machine.

Worked examples, step by step

Both examples below are three-phase, since the single-phase arithmetic is already covered above. Every intermediate value is shown so the substitution can be followed and checked by hand.

Example 1: kilowatts to amps, three-phase

A 45 kW chiller runs on a 480 V three-phase supply at a power factor of 0.88. What current does it draw per line?

A = (kW × 1000) / (√3 × V × PF)

1
Convert kilowatts to watts.
45 × 1000 = 45,000 W
2
Multiply √3 by the line-to-line voltage.
1.7320508 × 480 = 831.38
3
Apply the power factor.
831.38 × 0.88 = 731.62
4
Divide watts by that denominator.
45,000 / 731.62 = 61.51 A

Cross-check: at a power factor of 0.88 the apparent power is 45 / 0.88 = 51.14 kVA, which is the figure a transformer or generator feeding this load would need to supply.

Example 2: amps to kilowatts, three-phase

A clamp meter reads 75 A on each line of a 400 V three-phase motor circuit with a power factor of 0.92. How much real power is the motor drawing?

kW = (√3 × V × A × PF) / 1000

1
Multiply √3 by the line-to-line voltage.
1.7320508 × 400 = 692.82
2
Multiply by the measured line current.
692.82 × 75 = 51,961.52
3
Apply the power factor to get watts.
51,961.52 × 0.92 = 47,804.60 W
4
Divide by 1000 to reach kilowatts.
47,804.60 / 1000 = 47.80 kW

Cross-check: apparent power is 47.80 / 0.92 = 51.96 kVA, and the equivalent mechanical rating is 47.80 / 0.7457 = 64.11 HP before motor efficiency is taken into account.

kVA, HP, BTU and kWh quick converters

Four compact converters for the unit changes that do not involve voltage or phase count. Pick a tab, type a value, and the formula that produced the answer appears beneath it. The swap button reverses each conversion.

kVA

kW80.00

Power factor (0.01 to 1.00)

kW = kVA × PF
kW = 100 × 0.8 = 80.00 kW

What each conversion assumes

kVA ↔ kW: Needs the power factor, because apparent power and real power differ by exactly that ratio. At a power factor of 1.00 the two are identical.
HP ↔ kW: Uses mechanical (imperial) horsepower, where 1 HP is 0.7457 kW. The horsepower figure stamped on a motor's nameplate is shaft output, not electrical input, so nameplate data has to be divided by the machine's efficiency to get what the motor actually draws from the supply.
BTU/hr ↔ kW: One kilowatt is 3412.14 BTU per hour. Dividing BTU/hr by 12,000 gives tons of refrigeration, the unit HVAC equipment is usually rated in.
kWh ↔ kW: Needs a run time, since it crosses between power and energy. A load in kW multiplied by hours gives kWh; energy divided by hours gives average power.

All four formulas

kW = kVA × PF
kW = HP × 0.7457
kW = BTU/hr / 3412.14
kW = kWh / hours

How much power does a home or small business need?

The figures below are widely-quoted typical estimates used for rough planning. They are not measurements of any particular property, and they are not a substitute for a load calculation. Actual demand varies enormously with heating and cooling type, climate, insulation, occupancy, and whether there is an electric vehicle on the driveway. A house with a heat pump and a 48 A charger can draw several times what an otherwise identical gas-heated house draws.

As a starting point, a two-bedroom home is often estimated at a peak demand near 30 A, a three-bedroom home near 45 A, and a small business somewhere between 50 A and 100 A. At the 240 V that North American residential service supplies, those currents correspond to roughly 7.2 kW, 10.8 kW and 12 to 24 kW respectively. Commercial premises are more often fed at 208 V or 480 V three-phase, where the same kilowatt figure corresponds to a much lower current per line.

Typical current and estimated power by application: reference estimates only
Location / application	Typical current	Voltage	Assumed PF	Estimated power
Two-bedroom home (whole-house peak)	~30 A	240 V	1.00	~7.2 kW
Three-bedroom home (whole-house peak)	~45 A	240 V	1.00	~10.8 kW
Small business premises	50 to 100 A	240 V	0.90	~10.8 to 21.6 kW
Level 2 EV charger	32 A	240 V	1.00	7.7 kW
Central air conditioner (3 ton)	~15 A	240 V	0.90	~3.2 kW
Electric water heater	18.8 A	240 V	1.00	4.5 kW
Electric range	40 A	240 V	1.00	9.6 kW
Electric clothes dryer	24 A	240 V	1.00	5.8 kW

Two effects keep the whole-property figure below the sum of the rows. Not every load runs at once, which is what a demand factor accounts for, and many loads cycle rather than run continuously. Adding every nameplate rating together therefore overstates real peak demand, often substantially.

General reference

Sizing a generator from a kW load

Generators carry two ratings, and the difference between them is the first thing that trips people up. The kW rating describes the real power the engine can produce; the kVA rating describes the apparent power the alternator can deliver. The two are linked by the power factor the set is rated at, commonly 0.8 for three-phase units, so a 100 kVA generator rated at 0.8 supplies 80 kW of real power. Feed it a load with a worse power factor than it was rated for and the available real power drops, even though the engine has capacity to spare, because the alternator windings reach their current limit first. The steady current a set can sustain at its rated voltage is its generator full-load amps, and that figure, rather than the momentary surge it can absorb, is what feeder and protective-device selection works from.

A common planning convention is to choose a set so the expected continuous running load falls somewhere between 50% and 80% of its continuous rating. The upper bound leaves headroom for load growth and for transient surges; the lower bound matters too, because running a diesel set very lightly loaded for extended periods is generally discouraged by manufacturers.

Motor starting is usually the deciding factor rather than steady-state load. An induction motor draws roughly 6 to 8 times its full-load running current at the instant of starting, because at standstill there is no back-EMF opposing the supply. The surge lasts only until the rotor comes up to speed, but while it lasts it drags the bus voltage down (a momentary sag known as a voltage dip), and a generator has to ride through that without its voltage or frequency collapsing far enough to drop other connected equipment. This is why a set sized purely on running kilowatts can prove badly undersized in practice, and why soft starters and variable-frequency drives change the sizing picture considerably.

Working the other way, adding up every nameplate on a property overstates the real peak, because not everything runs simultaneously. This is what a demand factor expresses: the ratio of actual maximum demand to total connected load. Article 220 of the National Electrical Code (NEC) sets out demand factors and standard load calculation methods used in the United States for exactly this reason. Codes differ between jurisdictions, and they are revised periodically.

This section is general reference information, not installation guidance. The figures above are conventions and rules of thumb for understanding how generator sizing works. They are not sufficient on their own to select equipment. Actual generator sizing, transfer-switch selection, breaker sizing, conductor and wire-gauge selection, and code compliance for a specific installation must be carried out by a licensed electrician or a qualified engineer working from the real connected load, the applicable edition of the local electrical code, and the site conditions. Nothing on this page should be treated as a substitute for that.

FAQ

Frequently asked questions

Answers to the questions people ask most before and while using this calculator.

Conversions

How many amps is 1 kW at 120V?

1 kW at 120 V single-phase draws about 8.33 amps at a power factor of 1.0. The arithmetic is (1 × 1000) ÷ (120 × 1.0) = 8.33 A. If the load is inductive rather than purely resistive (a small motor at a power factor of 0.85, say), the same kilowatt pulls more current, about 9.80 A.

How many amps is 1 kW at 240V?

1 kW at 240 V single-phase draws about 4.17 amps at a power factor of 1.0. That is (1 × 1000) ÷ (240 × 1.0) = 4.17 A, exactly half the current the same kilowatt draws at 120 V. Doubling the voltage halves the current needed to move a given amount of power, which is the reason large appliances are wired at 240 V.

How do I convert kW to amps for three-phase?

Multiply the line-to-line voltage by √3 and the power factor, then divide watts by the result: A = (kW × 1000) ÷ (1.732 × V × PF). For 30 kW at 400 V with a power factor of 0.9, that is 30,000 ÷ (1.732 × 400 × 0.9) = 48.11 A. Use the line-to-neutral form with a multiplier of 3 instead of √3 if the voltage you measured was phase-to-neutral.

How many kW is 100 amps at 240V?

100 amps at 240 V single-phase is 24 kW at a power factor of 1.0. The formula is (240 × 100 × 1.0) ÷ 1000 = 24 kW. At a power factor of 0.9 the same 100 amps delivers only 21.6 kW of real power, because part of the current is circulating as reactive power rather than doing work.

Can kilowatts be converted to amps without knowing voltage?

No. Voltage is required, because amps measure the rate of charge flow while kilowatts measure the rate of energy transfer, and voltage is the term that links the two. Without it, one kilowatt figure maps to infinitely many current values. 10 kW is 41.67 A at 240 V but only 20.83 A at 480 V, both at unity power factor.

How do I convert kVA to kW?

Multiply kilovolt-amperes by the power factor: kW = kVA × PF. A 100 kVA transformer supplying a load at a power factor of 0.8 delivers 80 kW of real power. Going the other way you divide instead of multiply, so kVA = kW ÷ PF.

How do I convert kW to BTU per hour?

Multiply kilowatts by 3412.14 to get BTU per hour. A 5 kW electric heater produces 5 × 3412.14 = 17,060.7 BTU/hr. Dividing BTU/hr by 12,000 converts to tons of refrigeration, making that same 5 kW roughly 1.42 tons.

Formulas & Concepts

What is the formula to convert amps to kW?

For single-phase AC it is kW = (V × A × PF) ÷ 1000; for DC drop the power factor, and for three-phase multiply by √3 when using line-to-line voltage. The division by 1000 is only the step from watts to kilowatts. All four variants express the same physical relationship (power is voltage times current) with a phase-count multiplier and a power-factor correction applied.

What is power factor and why does it matter?

Power factor is the ratio of real power (kW) to apparent power (kVA): a number between 0 and 1 describing how much of the current is doing useful work. A load running at 0.7 power factor draws about 43% more current than the same real load at 1.0, which means larger conductors, a larger breaker, and on many commercial tariffs a utility surcharge.

What power factor should I use if I don't know it?

Use 0.8 as a working estimate for mixed loads that include motors, and 1.0 for purely resistive loads such as heaters, electric ovens and incandescent lamps. Both are rules of thumb for planning arithmetic rather than measured values. The equipment nameplate or a clamp meter reading gives the real figure, and the nameplate is what counts for anything that will actually be installed.

What's the difference between kW and kVA?

kW is real power, the portion that does useful work, while kVA is apparent power, the total the supply and its conductors have to carry. The two are equal only at a power factor of 1.0. Because cables and breakers respond to total current rather than useful output, equipment such as transformers, generators and UPS units is rated in kVA.

Is kW the same as kWh?

No. A kilowatt is a rate of power and a kilowatt-hour is a quantity of energy: one kilowatt sustained for one hour. A 2 kW heater running for 3 hours consumes 6 kWh. Utility bills are denominated in kWh because they charge for energy delivered over time, while cables and breakers are sized from kW and amps because those reflect the instantaneous rate.

What is reactive power?

Reactive power, measured in kVAR, is power that shuttles back and forth between the source and a load’s magnetic or electric fields without ever being converted into useful work. Motors and transformers need it to establish their magnetic fields. It ties to the other two quantities through the power triangle, where kVA² = kW² + kVAR².

What is the difference between Ohm's Law and Watt's Law?

Ohm's Law relates voltage, current and resistance as V = I × R, while Watt's Law relates power, voltage and current as P = V × I. Used together they let you solve for any one of the four quantities given two of the others, which is how a kilowatt figure can be traced back to a resistance in ohms.

Three-Phase

How do I calculate three-phase kW from amps?

Multiply √3 by the line-to-line voltage, the current and the power factor, then divide by 1000: kW = (1.732 × V × A × PF) ÷ 1000. For 40 amps at 208 V with a power factor of 0.85, that gives (1.732 × 208 × 40 × 0.85) ÷ 1000 = 12.25 kW.

What's the difference between line-to-line and line-to-neutral voltage?

Line-to-line voltage is measured between any two phase conductors, while line-to-neutral is measured between one phase conductor and the neutral. In a balanced wye system the line-to-line figure is √3 times the line-to-neutral figure, so a 480 V line-to-line system measures 277 V line-to-neutral. Mixing the two up is the most common three-phase calculation mistake.

Why does the three-phase formula use √3?

Because the three phases peak 120 electrical degrees apart, their contributions add vectorially rather than arithmetically, and the vector sum for a balanced set works out to √3 times the per-phase value. √3 is approximately 1.732. It appears whenever line-to-line voltage and line current are combined in the same expression.

Is the formula different for line-to-neutral voltage?

Yes, with line-to-neutral voltage the multiplier becomes 3 rather than √3, so kW = (3 × V × A × PF) ÷ 1000. Both forms return the same answer for the same physical circuit, because substituting line-to-line voltage = √3 × line-to-neutral voltage converts one into the other. Choose the form matching the voltage you actually measured.

What's a typical three-phase voltage in commercial buildings?

480 V line-to-line is the common commercial and industrial three-phase voltage in North America, with 208 V serving lighter building loads; most of Europe, the UK and much of Asia use 400 V. Their line-to-neutral counterparts are about 277 V, 120 V and 230 V respectively, which is how a single three-phase service can also feed ordinary single-phase circuits.

What is the difference between a delta and a wye connection?

In a delta connection the three windings form a closed triangle with no neutral point, while in a wye, also called star, one end of each winding joins at a common neutral. Wye offers two usable voltages plus a neutral for single-phase loads, which suits building distribution. Delta carries no neutral and is common on motors and on the primary side of distribution transformers.

Does a three-phase motor's kW rating already account for power factor?

No. A motor nameplate kW is its mechanical output at the shaft, so it accounts for neither power factor nor efficiency on the electrical input side. To estimate the current it will really draw, first divide the nameplate kW by the efficiency to get input power, then apply the three-phase formula using the nameplate power factor.

Sizing & Real-World

How many kW does a two-bedroom house use?

A two-bedroom home is commonly estimated at a peak demand of around 30 amps, which is roughly 7.2 kW at 240 V. That is a widely-quoted planning estimate rather than a measurement of any particular house. Real demand swings with heating type, climate and appliance mix, and a licensed electrician performs the actual load calculation for a service.

How many kW does a three-bedroom house use?

A three-bedroom home is commonly estimated at around 45 amps, roughly 10.8 kW at 240 V. Again this is a typical figure for rough planning only. An all-electric home with a heat pump and an EV charger can draw considerably more, which is why service sizing is based on a formal load calculation rather than a bedroom count.

What size generator do I need for my home?

As general reference, a generator is usually chosen so the expected running load falls between 50% and 80% of its continuous rating, leaving headroom for motor starting surges. Because generators carry a kVA rating as well as a kW rating, a low power factor reduces the real power actually available. A licensed electrician should size the set and the transfer equipment for any real installation.

How do I calculate electricity cost from kW?

Multiply the load in kW by the hours it runs to get kWh, then multiply that by your tariff rate. A 9.6 kW electric range used for 3 hours at $0.17 per kWh costs 9.6 × 3 × 0.17 = $4.90. Only the rate printed on your own bill gives an accurate result, since tariffs vary by region and by time of day.

How do I convert horsepower to kilowatts for a motor?

Multiply horsepower by 0.7457, so a 25 HP motor is 18.64 kW. That result is mechanical output power. Electrical input is higher by the motor’s efficiency, so the same 25 HP motor running at 92% efficiency draws about 20.26 kW from the supply.

Why does a motor draw more current when it starts?

A motor at standstill generates no back-EMF to oppose the supply, so inrush current typically reaches 6 to 8 times the full-load running current for a brief moment. The surge lasts only until the rotor comes up to speed, but it is the reason generator and protective-device selection considers starting current rather than running load alone.

How many amps does an EV charger draw?

A typical Level 2 home charger delivers 7.7 kW at 32 amps on 240 V, while larger units run at 48 amps for about 11.5 kW. In Europe a three-phase 400 V wallbox rated 11 kW draws about 15.9 A per phase at unity power factor, and a 22 kW unit about 31.8 A. Continuous loads like these are a common reason an existing service needs reassessing.

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