Find the voltage a circuit must be operating at, given its real power, measured current and power factor.
If you have the supply rating rather than the current, start with the kVA to kW calculator.
Every diagram and table on this page updates with the calculator above.
In practice voltage is set by the supply, not derived from power. This calculation earns its place as a cross-check: if a set of measurements does not produce a plausible voltage, one of them is wrong.
Supply voltages are standardised. If your answer is nowhere near one of them, the inputs deserve another look before the conclusion does.
| Nominal | Where it is used | Typical tolerance |
|---|---|---|
| 120 V | North American single phase | ±5% |
| 208 V | North American three phase (wye) | ±5% |
| 230 V | European single phase | +10% / −6% |
| 400 / 415 V | European three phase | ±10% |
| 480 V | North American industrial | ±10% |
| 690 V | Large industrial plant | ±10% |
Power values converted at your measured current, power factor and supply type.
| kW | Voltage (V) | Apparent power (kVA) |
|---|---|---|
| 1 kW | 7.5 | 1.11 |
| 2 kW | 15.1 | 2.22 |
| 5 kW | 37.7 | 5.56 |
| 7.5 kW | 56.6 | 8.33 |
| 10 kW | 75.5 | 11.11 |
| 15 kW | 113.2 | 16.67 |
| 22 kW | 166 | 24.44 |
| 30 kW | 226.4 | 33.33 |
| 45 kW | 339.6 | 50 |
| 55 kW | 415.1 | 61.11 |
| 75 kW | 566 | 83.33 |
| 90 kW | 679.2 | 100 |
| 110 kW | 830.2 | 122.22 |
| 150 kW | 1,132.1 | 166.67 |
| 200 kW | 1,509.4 | 222.22 |
| 300 kW | 2,264.1 | 333.33 |
A 400 V board measuring 392 V under load is entirely normal. Supply tolerance, transformer tap position and volt drop along the cable all contribute.
Cable tables give the mV/A/m figure for each conductor size.
| Circuit type | Typical limit | At 400 V |
|---|---|---|
| Lighting | 3% | 12 V |
| Power circuits | 5% | 20 V |
| Motor starting (transient) | 10–15% | 40–60 V |
A motor delivering fixed mechanical power at reduced voltage draws more current to compensate, running hotter and shortening its insulation life.
Read across or down to see how sensitive the answer is to each measurement — and how quickly a small current error moves the result.
| kW | 20 A | 50 A | 85 A | 125 A | 200 A |
|---|---|---|---|---|---|
| 5 kW | 160 | 64 | 38 | 26 | 16 |
| 15 kW | 481 | 192 | 113 | 77 | 48 |
| 30 kW | 962 | 385 | 226 | 154 | 96 |
| 50 kW | 1,604 | 642 | 377 | 257 | 160 |
| 75 kW | 2,406 | 962 | 566 | 385 | 241 |
| 110 kW | 3,528 | 1,411 | 830 | 565 | 353 |
| 160 kW | 5,132 | 2,053 | 1,208 | 821 | 513 |
Check a set of readings against each other before trusting them for a design decision.
Work out the intended supply for a machine whose nameplate is missing or illegible.
Confirm that a drive or motor is seeing the voltage the commissioning sheet claims.
29 calculators built on the same maths as the tool above. Each one has its own inputs, interactive diagrams and worked examples.
Common questions about converting kw to volts.