Calculate steady operating current, power or voltage for DC, single-phase AC and balanced three-phase AC. Select electrical input or motor shaft-output power; enter true power factor and motor efficiency where applicable. Breaker and conductor sizing require a separate installation-specific design.
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Current From kW Formula
For steady DC, or single-phase AC at unity PF, use electrical real-input power in the following formula. The examples and table below use these assumptions.
- Where Ikw is the Current From kW (amps)
- KW is electrical real-input power (kW), not motor shaft output
- V is the total voltage (volts)
For DC, I = 1,000 × input kW / V. For single-phase AC, divide additionally by true PF. For balanced three-phase AC, use total input power and divide by √3 × line-to-line RMS voltage × true PF, or 3 × line-to-neutral RMS voltage × true PF. If the specified power is motor shaft output, first divide by motor efficiency to obtain electrical input. These equations calculate operating current, not starting current or breaker/wire ratings.
| Power (kW) | Amps @ 120 V | Amps @ 208 V | Amps @ 230 V | Amps @ 240 V | Amps @ 277 V | Amps @ 480 V |
|---|---|---|---|---|---|---|
| 0.25 | 2.08 | 1.20 | 1.09 | 1.04 | 0.90 | 0.52 |
| 0.50 | 4.17 | 2.40 | 2.17 | 2.08 | 1.80 | 1.04 |
| 0.75 | 6.25 | 3.61 | 3.26 | 3.13 | 2.71 | 1.56 |
| 1 | 8.33 | 4.81 | 4.35 | 4.17 | 3.61 | 2.08 |
| 1.5 | 12.50 | 7.21 | 6.52 | 6.25 | 5.42 | 3.13 |
| 2 | 16.67 | 9.62 | 8.70 | 8.33 | 7.22 | 4.17 |
| 3 | 25.00 | 14.42 | 13.04 | 12.50 | 10.83 | 6.25 |
| 4 | 33.33 | 19.23 | 17.39 | 16.67 | 14.44 | 8.33 |
| 5 | 41.67 | 24.04 | 21.74 | 20.83 | 18.05 | 10.42 |
| 7.5 | 62.50 | 36.06 | 32.61 | 31.25 | 27.08 | 15.63 |
| 10 | 83.33 | 48.08 | 43.48 | 41.67 | 36.10 | 20.83 |
| 12.5 | 104.17 | 60.10 | 54.35 | 52.08 | 45.13 | 26.04 |
| 15 | 125.00 | 72.12 | 65.22 | 62.50 | 54.15 | 31.25 |
| 20 | 166.67 | 96.15 | 86.96 | 83.33 | 72.20 | 41.67 |
| 25 | 208.33 | 120.19 | 108.70 | 104.17 | 90.25 | 52.08 |
| 30 | 250.00 | 144.23 | 130.43 | 125.00 | 108.30 | 62.50 |
| 40 | 333.33 | 192.31 | 173.91 | 166.67 | 144.41 | 83.33 |
| 50 | 416.67 | 240.38 | 217.39 | 208.33 | 180.51 | 104.17 |
| 75 | 625.00 | 360.58 | 326.09 | 312.50 | 270.76 | 156.25 |
| 100 | 833.33 | 480.77 | 434.78 | 416.67 | 361.01 | 208.33 |
| Formula: I (A) = P (kW) × 1000 / V (V). Assumes single‑phase/DC and power factor PF = 1.00. | ||||||
How to Calculate Current From kW?
The following two example problems outline how to calculate the Current From kW.
Example Problem #1:
- First, determine the total kilowatts (kW). In this example, the total kilowatts (kW) is measured to be 5.
- Next, determine the total voltage (volts). For this problem, the total voltage (volts) is calculated to be 100.
- Finally, calculate the Current From kW using the formula above:
Ikw = KW *1000 / V
Inserting the values from above and solving the equation with the imputed values gives:
Ikw = 5 *1000 / 100 = 50 (amps)
Example Problem #2:
Using the same process as example problem 1, we first define the variables outlined by the formula. In this case, the values are:
total kilowatts (kW) = 3
total voltage (volts) = 50
Entering these values into the formula above gives us
Ikw = 3*1000 / 50 = 60 (amps)
