kW equals kVA times power factor. Reactive power is the part that does no work but still heats the conductors, which is why transformers are rated in kVA rather than kW. Power factor of 0.9 is a reasonable default for a mixed commercial load, but use the real figure if you have it.
kVA to kW for common sizes
Real power at the four power factors that cover almost every building. Unity power factor is the ceiling, kW can never exceed kVA.
| kVA | PF 1.0 | PF 0.9 | PF 0.85 | PF 0.8 | MVA |
|---|---|---|---|---|---|
| 5 | 5 kW | 4.5 kW | 4.3 kW | 4 kW | 0.005 |
| 10 | 10 kW | 9 kW | 8.5 kW | 8 kW | 0.01 |
| 15 | 15 kW | 13.5 kW | 12.8 kW | 12 kW | 0.015 |
| 20 | 20 kW | 18 kW | 17 kW | 16 kW | 0.02 |
| 25 | 25 kW | 22.5 kW | 21.3 kW | 20 kW | 0.025 |
| 30 | 30 kW | 27 kW | 25.5 kW | 24 kW | 0.03 |
| 37.5 | 37.5 kW | 33.8 kW | 31.9 kW | 30 kW | 0.0375 |
| 45 | 45 kW | 40.5 kW | 38.3 kW | 36 kW | 0.045 |
| 50 | 50 kW | 45 kW | 42.5 kW | 40 kW | 0.05 |
| 60 | 60 kW | 54 kW | 51 kW | 48 kW | 0.06 |
| 70 | 70 kW | 63 kW | 59.5 kW | 56 kW | 0.07 |
| 75 | 75 kW | 67.5 kW | 63.8 kW | 60 kW | 0.075 |
| 100 | 100 kW | 90 kW | 85 kW | 80 kW | 0.1 |
| 112.5 | 112.5 kW | 101.3 kW | 95.6 kW | 90 kW | 0.1125 |
| 125 | 125 kW | 112.5 kW | 106.3 kW | 100 kW | 0.125 |
| 150 | 150 kW | 135 kW | 127.5 kW | 120 kW | 0.15 |
| 200 | 200 kW | 180 kW | 170 kW | 160 kW | 0.2 |
| 225 | 225 kW | 202.5 kW | 191.3 kW | 180 kW | 0.225 |
| 250 | 250 kW | 225 kW | 212.5 kW | 200 kW | 0.25 |
| 300 | 300 kW | 270 kW | 255 kW | 240 kW | 0.3 |
| 400 | 400 kW | 360 kW | 340 kW | 320 kW | 0.4 |
| 450 | 450 kW | 405 kW | 382.5 kW | 360 kW | 0.45 |
| 500 | 500 kW | 450 kW | 425 kW | 400 kW | 0.5 |
| 600 | 600 kW | 540 kW | 510 kW | 480 kW | 0.6 |
| 750 | 750 kW | 675 kW | 637.5 kW | 600 kW | 0.75 |
| 900 | 900 kW | 810 kW | 765 kW | 720 kW | 0.9 |
| 1000 | 1,000 kW | 900 kW | 850 kW | 800 kW | 1 |
| 1500 | 1,500 kW | 1,350 kW | 1,275 kW | 1,200 kW | 1.5 |
| 2000 | 2,000 kW | 1,800 kW | 1,700 kW | 1,600 kW | 2 |
| 2500 | 2,500 kW | 2,250 kW | 2,125 kW | 2,000 kW | 2.5 |
Free to cite with a link to this page. kW is kVA times power factor and MVA is kVA divided by 1000. The three phase formulas page has the rest, including current and fault current.
Typical power factors
| Power factor | Typical of | 300 kVA gives |
|---|---|---|
| 1.0 | Resistive heating, incandescent lighting | 300 kW |
| 0.95 | Modern LED lighting, corrected commercial load | 285 kW |
| 0.9 | Typical mixed commercial building | 270 kW |
| 0.85 | Light industrial with motors | 255 kW |
| 0.8 | Motor heavy industrial, uncorrected | 240 kW |
Free to cite with a link to this page. The spread between 0.8 and 0.95 on the same 300 kVA transformer is 45 kW of real power, which is frequently a whole transformer size in a sizing exercise.
Common questions
What does kVA mean on a transformer
Kilovolt amperes, which is apparent power. It is voltage times current with no allowance for power factor. Transformers are rated in kVA because heating depends on current regardless of whether that current is doing useful work, and heating is what limits the machine.
How do you convert kVA to kW
Multiply kVA by the power factor. A 300 kVA transformer at a power factor of 0.9 delivers 270 kW of real power. To go the other way, divide kW by the power factor.
Why are transformers rated in kVA and not kW
Because the transformer does not know what the load is doing with the current. Reactive current heats the windings exactly as much as real current does, so the limit is total current, which is apparent power. Rating in kW would mean the same transformer had a different rating for every load connected to it.
What is a typical power factor
Around 0.9 for a mixed commercial building, 0.85 or lower for motor heavy industrial, and close to 1.0 for resistive loads such as heating. Use the measured figure where you have one, because the difference between 0.8 and 0.95 is a whole transformer size.
Sizing a transformer from a service rating instead. Use the sizing calculator, or the kVA to amps calculator for current. Starting from a load in kW, the kW to amps calculator gives the current directly. For a motor load, the HP to kVA calculator starts from horsepower. To move between kVA, MVA, kW and MW, or kWh and MWh, use the kW to MW converter. To size a small unit that fixes a 208 to 240 volt mismatch, use the buck boost transformer calculator.