Turn a clamp-meter current reading into the real power a circuit is actually consuming.
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.
Same expression with the √3 removed.
Without a power factor you can only reach kVA. Current and voltage alone tell you what the supply is carrying, never how much of it is doing work.
A clamp meter reads current magnitude, not its phase relationship to voltage. Two circuits with identical current can consume very different amounts of power.
Move the power factor slider: the current wave slides out of step with voltage while its height stays exactly the same. That shift is invisible to a basic clamp meter.
On circuits with drives, rectifiers or LED drivers, an averaging meter can read 10–40% low. Use a true-RMS instrument on anything non-linear.
Enclosing two conductors gives the vector sum, which on a balanced pair is close to zero.
Unbalance is common. Use the highest reading for cable checks and the average for an energy estimate.
Supply voltage moves through the day; pairing a morning current with an evening voltage introduces error.
Use a power analyser if you can. Otherwise take it from the motor nameplate at the observed loading.
A reading taken during a lull is not the design figure. Capture the peak you actually need to size for.
If your calculated kW exceeds the equipment rating, one of the inputs is wrong — usually the power factor or a clamp around the wrong conductor.
Standard breaker-sized current readings converted at your voltage, power factor and supply type.
| A | Real power (kW) | Apparent power (kVA) |
|---|---|---|
| 5 A | 2.94 | 3.46 |
| 10 A | 5.89 | 6.93 |
| 16 A | 9.42 | 11.09 |
| 20 A | 11.78 | 13.86 |
| 25 A | 14.72 | 17.32 |
| 32 A | 18.84 | 22.17 |
| 40 A | 23.56 | 27.71 |
| 63 A | 37.1 | 43.65 |
| 80 A | 47.11 | 55.43 |
| 100 A | 58.89 | 69.28 |
| 125 A | 73.61 | 86.6 |
| 160 A | 94.22 | 110.85 |
| 200 A | 117.78 | 138.56 |
| 250 A | 147.22 | 173.21 |
| 400 A | 235.56 | 277.13 |
| 630 A | 371.01 | 436.48 |
Useful when you know the breaker size but not the supply arrangement — read across to compare voltages at a glance.
| A | 230 V | 400 V | 415 V | 480 V |
|---|---|---|---|---|
| 16 A | 5.4 | 9.4 | 9.8 | 11.3 |
| 32 A | 10.8 | 18.8 | 19.6 | 22.6 |
| 63 A | 21.3 | 37.1 | 38.5 | 44.5 |
| 100 A | 33.9 | 58.9 | 61.1 | 70.7 |
| 160 A | 54.2 | 94.2 | 97.8 | 113.1 |
| 250 A | 84.7 | 147.2 | 152.7 | 176.7 |
| 400 A | 135.4 | 235.6 | 244.4 | 282.7 |
Utilities bill energy in kilowatt-hours and often charge separately for peak demand and for poor power factor. All three numbers come from the same measurement.
| Quantity | From this calculation | Where it appears |
|---|---|---|
| Real power | kW | Energy charge, once multiplied by hours |
| Apparent power | kVA | Maximum demand charge on many tariffs |
| Reactive power | kVAR | Power factor penalty or kVArh charge |
The gap between the two bars is capacity your supply carries without earning anything — the exact quantity that power factor correction removes.
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 amps to kw.