Three phase amps equal kW times 1000 divided by root 3 times line to line volts times power factor. Single phase drops the root 3. DC drops the power factor too. Transformers are sized on the kVA figure, not the kW figure.
The formulas
| System | kW to amps | Amps to kW |
|---|---|---|
| Three phase | A = kW x 1000 / (1.732 x V x PF) | kW = A x 1.732 x V x PF / 1000 |
| Single phase | A = kW x 1000 / (V x PF) | kW = A x V x PF / 1000 |
| DC | A = kW x 1000 / V | kW = A x V / 1000 |
V is line to line voltage on three phase, so 480 on a 480Y/277 system and 208 on a 208Y/120 system. PF is power factor, a number between 0 and 1. The most common mistake is using the single phase formula on a three phase load, which overstates the current by a factor of 1.732.
Amps per kW by voltage
Multiply your kW by the figure in the row for your voltage. At 480 V three phase and unity power factor every kW draws 1.20 A.
| System | PF 1.00 | PF 0.90 | PF 0.85 | PF 0.80 |
|---|---|---|---|---|
| 120 V single phase | 8.33 A | 9.26 A | 9.80 A | 10.42 A |
| 208 V three phase | 2.78 A | 3.08 A | 3.27 A | 3.47 A |
| 240 V single phase | 4.17 A | 4.63 A | 4.90 A | 5.21 A |
| 240 V three phase | 2.41 A | 2.67 A | 2.83 A | 3.01 A |
| 277 V single phase | 3.61 A | 4.01 A | 4.25 A | 4.51 A |
| 400 V three phase | 1.44 A | 1.60 A | 1.70 A | 1.80 A |
| 480 V three phase | 1.20 A | 1.34 A | 1.42 A | 1.50 A |
| 600 V three phase | 0.96 A | 1.07 A | 1.13 A | 1.20 A |
Free to cite with a link to this page. Every figure is computed from the formulas above.
kW to amps chart, three phase
Current per phase at a power factor of 0.85, about what a fully loaded induction motor runs at. The last column is the kVA the load needs and the smallest standard three phase transformer that covers it.
| kW | 208 V | 240 V | 480 V | 600 V | kVA | Transformer |
|---|---|---|---|---|---|---|
| 1 | 3.3 A | 2.8 A | 1.4 A | 1.1 A | 1.2 | 45 kVA |
| 5 | 16.3 A | 14.2 A | 7.1 A | 5.7 A | 5.9 | 45 kVA |
| 7.5 | 24.5 A | 21.2 A | 10.6 A | 8.5 A | 8.8 | 45 kVA |
| 10 | 32.7 A | 28.3 A | 14.2 A | 11.3 A | 11.8 | 45 kVA |
| 15 | 49.0 A | 42.5 A | 21.2 A | 17.0 A | 17.6 | 45 kVA |
| 20 | 65.3 A | 56.6 A | 28.3 A | 22.6 A | 23.5 | 45 kVA |
| 25 | 81.6 A | 70.8 A | 35.4 A | 28.3 A | 29.4 | 45 kVA |
| 30 | 98.0 A | 84.9 A | 42.5 A | 34.0 A | 35.3 | 45 kVA |
| 40 | 131 A | 113 A | 56.6 A | 45.3 A | 47.1 | 75 kVA |
| 50 | 163 A | 142 A | 70.8 A | 56.6 A | 58.8 | 75 kVA |
| 60 | 196 A | 170 A | 84.9 A | 67.9 A | 70.6 | 75 kVA |
| 75 | 245 A | 212 A | 106 A | 84.9 A | 88.2 | 112.5 kVA |
| 100 | 327 A | 283 A | 142 A | 113 A | 118 | 150 kVA |
| 125 | 408 A | 354 A | 177 A | 142 A | 147 | 150 kVA |
| 150 | 490 A | 425 A | 212 A | 170 A | 176 | 225 kVA |
| 200 | 653 A | 566 A | 283 A | 226 A | 235 | 300 kVA |
| 250 | 816 A | 708 A | 354 A | 283 A | 294 | 300 kVA |
| 300 | 980 A | 849 A | 425 A | 340 A | 353 | 500 kVA |
| 400 | 1,306 A | 1,132 A | 566 A | 453 A | 471 | 500 kVA |
| 500 | 1,633 A | 1,415 A | 708 A | 566 A | 588 | 750 kVA |
| 600 | 1,959 A | 1,698 A | 849 A | 679 A | 706 | 750 kVA |
| 750 | 2,449 A | 2,123 A | 1,061 A | 849 A | 882 | 1000 kVA |
| 800 | 2,612 A | 2,264 A | 1,132 A | 906 A | 941 | 1000 kVA |
| 1000 | 3,266 A | 2,830 A | 1,415 A | 1,132 A | 1,176 | 1500 kVA |
| 1250 | 4,082 A | 3,538 A | 1,769 A | 1,415 A | 1,471 | 1500 kVA |
| 1500 | 4,898 A | 4,245 A | 2,123 A | 1,698 A | 1,765 | 2000 kVA |
| 2000 | 6,531 A | 5,660 A | 2,830 A | 2,264 A | 2,353 | 2500 kVA |
| 2500 | 8,164 A | 7,075 A | 3,538 A | 2,830 A | 2,941 | over 2500 |
Free to cite with a link to this page. For unity power factor loads such as resistive heat, multiply any figure by 0.85. The transformer column is the next standard pad mounted rating and leaves no room for growth, so check it with the sizing calculator.
kW to amps chart, single phase
| kW | 120 V, PF 1.0 | 120 V, PF 0.85 | 240 V, PF 1.0 | 240 V, PF 0.85 |
|---|---|---|---|---|
| 1 | 8.3 A | 9.8 A | 4.2 A | 4.9 A |
| 1.5 | 12.5 A | 14.7 A | 6.3 A | 7.4 A |
| 2 | 16.7 A | 19.6 A | 8.3 A | 9.8 A |
| 3 | 25.0 A | 29.4 A | 12.5 A | 14.7 A |
| 5 | 41.7 A | 49.0 A | 20.8 A | 24.5 A |
| 7.5 | 62.5 A | 73.5 A | 31.3 A | 36.8 A |
| 10 | 83.3 A | 98.0 A | 41.7 A | 49.0 A |
| 12 | 100 A | 118 A | 50.0 A | 58.8 A |
| 15 | 125 A | 147 A | 62.5 A | 73.5 A |
| 20 | 167 A | 196 A | 83.3 A | 98.0 A |
| 25 | 208 A | 245 A | 104 A | 123 A |
| 30 | 250 A | 294 A | 125 A | 147 A |
| 40 | 333 A | 392 A | 167 A | 196 A |
| 50 | 417 A | 490 A | 208 A | 245 A |
Free to cite with a link to this page.
kW, kVA and why power factor matters
kW is real power, the part that turns a shaft or heats a room. kVA is apparent power, volts times amps, and it is what wires, breakers and transformers actually carry. The two are equal only at a power factor of 1.0. Below that, kVA equals kW divided by power factor, so a 100 kW load at 0.8 needs 125 kVA of transformer. The kVA to kW calculator converts between the two, and the kVA to amps calculator gives current straight from a transformer rating.
| Load | Typical power factor |
|---|---|
| Resistive heating, incandescent lamps | 1.0 |
| Fluorescent lamps with compensation | about 0.93 |
| Induction motor at full load | about 0.85 |
| Induction motor at half load | about 0.73 |
| Induction motor at a quarter load | about 0.55 |
| Uncorrected industrial plant | about 0.8 |
| Fluorescent lamps without compensation | about 0.5 |
Typical values from the published sources listed at the end of this page. A lightly loaded motor draws more current per kW than a fully loaded one, so measure where you can.
Picking a transformer from a kW load
Divide the total kW by the power factor to get kVA, then choose the next standard rating up. A 400 kW load at 0.85 is 471 kVA, which points to a 500 kVA pad mounted transformer. The three phase formulas page covers primary current, turns ratio and fault current, and the transformers for sale page lists every standard rating we quote. The commercial service sizes chart maps each service from 100 to 4000 A to its transformer, and the grow light circuit calculator works out lights per breaker and the monthly cost for a grow room. For a motor load, the HP to kVA calculator converts horsepower to the kVA to size from.
Common questions
How do you convert kW to amps in three phase
Multiply kW by 1000 to get watts, then divide by root 3 (1.732), the line to line voltage and the power factor. A 100 kW load at 480 V and a power factor of 0.85 draws 142 A per phase.
How many amps is 100 kW at 480 volts
142 A at a power factor of 0.85, and 120 A at unity power factor, three phase. The lower the power factor the more current the same kW needs.
How many amps is 10 kW three phase
At 208 V and a power factor of 0.85 it is 32.7 A. At 480 V it is 14.2 A. Use the chart above for other voltages.
How many amps is 7.5 kW single phase
At 240 V and unity power factor, such as a resistive heater, it is 31.3 A. At 120 V it is 62.5 A.
How do you convert amps to kW
Reverse the formula. Three phase kW equals amps times root 3 times volts times power factor, divided by 1000. So 200 A at 480 V and a power factor of 0.85 is 141 kW.
Why does power factor change the amps
Real power in kW is only the part of the current that does work. A load with a low power factor draws extra reactive current on top, so it needs more amps for the same kW. Wires, breakers and transformers have to carry the total current, which is why they are sized in amps and kVA.
What power factor should I use
Use the nameplate or a measured figure if you have one. Published guidance puts resistive heating and incandescent lighting at 1.0, an induction motor at about 0.85 at full load falling to about 0.55 at a quarter load, and a typical uncorrected industrial plant at about 0.8.
Sources
- Schneider Electric, Electrical Installation Guide, practical values of power factor
- Eskom, power factor technical overview
- elec.training, kW to amps formulas for DC, single and three phase
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