Amps to kW Calculator
Convert amps to kilowatts for DC, single-phase, and three-phase circuits with power factor. Live calculator with formulas and examples.
Common conversions
| Input | Result |
|---|---|
| 15 A DC @ 12 V | 0.18 kW |
| 10 A @ 120 V (1Φ, PF 1) | 1.20 kW |
| 20 A @ 240 V (1Φ, PF 1) | 4.80 kW |
| 30 A @ 240 V (1Φ, PF 0.9) | 6.48 kW |
| 100 A @ 208 V (3Φ, PF 0.85) | 30.62 kW |
| 50 A @ 480 V (3Φ, PF 0.9) | 37.41 kW |
| 200 A @ 400 V (3Φ, PF 0.88) | 121.94 kW |
| 15 A @ 277 V (1Φ L-N, PF 1) | 4.16 kW |
The math behind it
- kW = (45 × 48) / 1000
- kW = 2,160 / 1000
Everything you need to know
How the amps-to-kW formula actually works
Amperes measure the rate of electron flow. Kilowatts measure the rate of energy delivery. To get from one to the other you need voltage, because power equals current times voltage. On a DC circuit that's the whole formula: multiply amps by volts and divide by 1000. On AC circuits the voltage and current waveforms can drift out of step with each other, so a power factor (PF) term corrects for the share of current that does no real work. A PF of 1.0 means voltage and current stay perfectly in phase, typical of a resistive heater or incandescent bulb. A PF of 0.7 to 0.9 is normal for motors and compressors, where the magnetizing current lags the voltage.
Three-phase circuits add one more variable: how the voltage was measured. If you read line-to-line voltage, the number printed on most industrial nameplates such as 208 V, 400 V, or 480 V, multiply by √3 (about 1.732). If you measured line-to-neutral (phase) voltage instead, multiply by 3. Mixing these up is the most common error in this kind of calculation, and it produces a result that's off by roughly 73%.
Turning breaker and nameplate amps into a real kW load
Electricians and facility managers convert amps to kW constantly when amperage is the only number on hand, such as a breaker rating on a panel schedule or a reading pulled from a clamp meter. Converting that figure to kW lets you compare it against a generator's rated output, a transformer's kVA capacity, or a utility service's demand limit. For panel load calculations under NEC Article 220, standard practice is to convert each circuit's amperage to kW or VA, add up the connected load, then apply the applicable demand factor before sizing the service.
Remember that a breaker's amp rating is a maximum, not the actual running current. A 20 A breaker protecting a 12 A load will show 12 A on a clamp meter, not 20 A. Always convert the measured or nameplate current, not the breaker size, unless you're deliberately calculating worst-case capacity.
Example: sizing a portable generator from panel amperage
Say a homeowner wants a portable generator to run three circuits during an outage. The panel schedule lists a well pump at 15 A, a refrigerator compressor at 6 A, and a furnace blower at 8 A, all on 120 V single-phase circuits with an estimated PF of 0.85 for the motor loads. Converting each: the pump draws about 1.53 kW, the refrigerator about 0.61 kW, and the furnace blower about 0.82 kW, for a combined 2.96 kW. Adding headroom for motor starting current, a 5,000-watt generator comfortably covers all three circuits at once.
Common applications
Field technicians measure amps with a clamp meter, then convert to kW to compare against the nameplate. A 4% deviation usually means a measurement error; 15% or more suggests a real load or supply problem.
Once you know amperage and voltage, kW tells you whether the upstream feeder, transformer, and utility service can carry the load with headroom.
Convert the breaker amperage on each transferred circuit to kW to confirm you stay between 50% and 80% of the genset's prime rating.
Inverters report AC output amps. Convert to kW to verify against the array's expected production for the time of day.
Common mistakes
Amps times volts gives volt-amps, not watts. On AC, multiply by PF (typically 0.8-0.95 for mixed loads) or you'll overstate kW by 5-30%.
On a 480 V three-phase circuit, applying the single-phase formula gives a number that's √3 too small. Pick the formula that matches the topology.
Calculators expect RMS amps. Oscilloscope readings of peak current are √2 higher for pure sinusoids, so using them inflates kW by 41%.
Most clamp meters display amps only, and some multiply by an assumed voltage to show VA, not watts. Unless the meter has a true-power mode with a voltage lead attached, you still need to apply the correct formula and power factor yourself.
Frequently asked questions
How many kW is 30 amps at 240 volts?+
7.2 kW at a power factor of 1.0. Drop the power factor to 0.9, typical for a mixed load, and real power falls to about 6.48 kW.
Is 1 amp always equal to 240 watts?+
No, that relationship only holds at exactly 240 V with a power factor of 1.0. Change either variable and the watts-per-amp figure changes too.
How do I convert amps to kW for a three-phase circuit?+
Multiply amps by voltage, by √3, and by the power factor, then divide by 1000. For example, 40 A at 480 V line-to-line with a PF of 0.87 works out to about 28.9 kW.
Do I need a power factor for a purely resistive load like a water heater?+
No, resistive loads have a power factor of 1.0, so the PF term drops out and kW equals volts times amps divided by 1000.
How many kW is 100 amps at 208 volts three-phase?+
About 32.4 kW at a power factor of 0.9, using the line-to-line formula with √3.
Can I convert DC amps to kW the same way as AC amps?+
No, DC has no power factor term, so 50 A at 24 V DC is simply 1.2 kW with no PF multiplier involved.
Why does my calculated kW differ from my utility meter reading?+
Because the meter measures real energy delivered over time, including line losses and a power factor that shifts minute to minute, while this calculator gives a single theoretical value from the amps and PF you enter.
What's the difference between converting amps to kW and amps to kVA?+
kW is real power and includes the power factor; kVA is apparent power and does not. A 50 A, 240 V load is 12 kVA regardless of PF, but only 9.6 kW at a PF of 0.8.
How many kW can a 20 amp, 120 volt circuit deliver?+
2.4 kW at full rated amperage and PF 1.0, though the NEC's 80% continuous-load rule limits sustained use to about 1.92 kW.
Does wire gauge change the amps-to-kW conversion?+
No, wire size only determines how much current a conductor can safely carry. It does not appear anywhere in the power formula itself.