Electrical current calculator

Examples

5.75 kW at 230 V and unity power factor is 25 A. At 400 V three phase and 0.9 power factor, 15 kW is about 24.1 A per phase when balanced.

Active and apparent power

Bills and nameplates may show kW or kVA. kW is active power; kVA is apparent power. Confusing them underestimates current when power factor is below one.

Single- and three-phase formulae

For active electrical power: I = P/(V·cosφ) for single phase and I = P/(√3·V·cosφ) for a balanced three-phase load. Enter line-to-line voltage for three phase. If the stated power is mechanical or output power, equipment efficiency must be allowed for first.

For the next part of the decision, see the guides to Cable sizing and Voltage drop.

Which power rating should you enter?

The current calculator uses active electrical input power in kW. If a motor nameplate gives mechanical output at the shaft, divide that output by efficiency to estimate electrical input before calculating current. Entering output power directly can underestimate amperes even with the correct power factor.

For a balanced three-phase load, 15 kW is the total across all three phases; do not multiply it by three again. Use the voltage between phases, typically 400 V in this example. At a power factor of 0.9, the result is about 24.06 A per phase. Single-phase calculations use the corresponding line-to-neutral voltage, such as 230 V.

The calculated current represents operation under the entered assumptions. It does not include motor starting, imbalance or harmonic distortion. Selecting cable and protection additionally requires information about the load and installation method: the ampere result should not be treated automatically as a circuit-breaker rating.