Kilowatts to Amps Calculator
An electrician pulling a permit for a new 7.5 kW electric range circuit needs one number before touching the panel schedule: how many amps that range will actually draw at 240 V, so the breaker and the conductor can be sized correctly the first time.
Live, no submit
Current
31.25A
Formula, live
A = (kW × 1000) / (V × PF)
A = (7.5 × 1000) / (240 × 1) = 31.25 A
Why this conversion matters on a job
A kilowatt figure on a nameplate or a spec sheet describes real power, the rate energy is being delivered, but a breaker, a conductor and a disconnect are all rated in amps. Nothing on a panel schedule reads directly in kilowatts, so the conversion isn't optional background math; it's the step that turns a load rating into a number the rest of the installation can actually be sized against.
The same kilowatt figure produces a different amp draw depending on the voltage and, for anything other than a purely resistive load, the power factor, which is why a single "kW to amps" ratio can't be memorized and applied everywhere.
Where the amps formula comes from
Watt's Law states power equals voltage times current: P = V × I. Solving that for current gives I = P / V, and swapping in kilowatts instead of watts adds the factor of 1000. For a load that isn't purely resistive, only the power-factor fraction of the apparent current is doing real work, so the full current drawn is higher than the "P = VI" arithmetic alone would suggest. The power factor goes into the denominator to account for it.
Three-phase circuits add one more term. Because the three phases peak 120° apart, a line-to-line voltage measurement already reflects a vector sum rather than a simple arithmetic one, so the formula divides by √3 × V × PF instead of just V × PF. The calculator above switches formulas automatically based on the circuit type selected.
Worked example: sizing the range circuit
7.5 kW electric range, 240 V single-phase, power factor 1.0 (resistive load).
- 1
Convert kW to watts and apply the formula
A = (7.5 × 1000) / (240 × 1.0)
- 2
Solve
A = 7500 / 240 = 31.25 A
- 3
Add a 125% continuous-load margin
31.25 × 1.25 = 39.06 A
- 4
Round up to the next standard breaker size
39.06 A → 40 A breaker
This is general reference arithmetic, not a substitute for a code-compliant load calculation: ranges carry their own NEC demand-factor rules, and a licensed electrician confirms the final breaker and conductor size.
Common 240 V circuits, kW to amps
Single-phase, 240 V, power factor 1.0: typical of resistive residential loads such as ranges, dryers and water heaters. Motor-driven loads run below unity power factor and draw more current than this table shows for the same kW.
| Load | Amps at 240 V |
|---|---|
| 1 kW | 4.17 A |
| 3 kW | 12.50 A |
| 5 kW | 20.83 A |
| 7.5 kW | 31.25 A |
| 10 kW | 41.67 A |
| 15 kW | 62.50 A |
| 20 kW | 83.33 A |
| 30 kW | 125.00 A |
Reference estimates only, not measured values. Confirm any real circuit against its own nameplate and power factor.
Other conversions from a kilowatt figure
Questions
Kilowatts to amps FAQ
Sizing questions that come up once a kW figure has to turn into a real breaker and conductor pick.
What size breaker do I need for a 7.5 kW circuit?
A 7.5 kW load at 240 V single-phase draws 31.25 A, and many electricians add a 125% continuous-load margin before picking a standard breaker size. 31.25 × 1.25 = 39.06 A, which rounds up to the next standard breaker rating of 40 A. Ranges carry their own NEC demand-factor rules, so confirm the applicable code section and any occupancy-specific factors before sizing a real installation.
Does a bigger appliance always need a bigger breaker?
No: breaker size tracks current, not kilowatts, and current depends on voltage and power factor too. A 10 kW load at 240 V draws less current than an 8 kW load at 120 V, because doubling the voltage roughly halves the amps for the same power. Two appliances with different kW ratings can land on the same breaker size once voltage is accounted for.
Why do amps go down when voltage goes up?
Because power is the product of voltage and current, so for a fixed power delivery, current has to shrink as voltage grows. It's the same relationship utilities use to justify high-voltage transmission lines. A 7.5 kW load draws 31.25 A at 240 V but only 15.625 A at 480 V. That is also why heavy 240 V appliances use noticeably thinner conductors than an equivalent 120 V circuit would need.
What happens if I use the wrong power factor for a breaker calculation?
Understating the power factor overstates the current, and overstating it understates the current: the second mistake is the dangerous one, because it can lead to an undersized breaker and conductor. Purely resistive loads such as ranges, water heaters and baseboard heat run at a power factor of 1.0, so no correction is needed there. Anything with a motor (a compressor, a pump, a blower) runs below 1.0 and needs its nameplate power factor, not an assumed one, for a real sizing calculation.
Is the amperage on an appliance label the same as its breaker size?
No. The nameplate current is what the appliance draws, while the breaker is sized above that figure to allow for the margin the circuit needs without nuisance-tripping. A 40 A breaker commonly serves a load that draws around 30-32 A once the standard margin is applied. Reading the two numbers as interchangeable is a common source of an undersized or oversized breaker pick.
How much safety margin should a breaker have over the calculated amps?
As general reference, a common approach is to size the breaker at least 125% above a continuous load’s calculated current, then round up to the next standard breaker rating. Standard ratings jump in fixed steps (15, 20, 25, 30, 35, 40 A and up), so the rounding step usually adds its own extra headroom on top of the 125% figure. A licensed electrician applies the exact NEC provisions and any load-specific demand factors for an actual installation.