Power conversion equations
Choose one task. The phase factor is 1 for DC and single-phase AC, and √3 for balanced three-phase AC.
S = P / PFP = S × PFI = S × 1000 / (Fphase × V)P = Fphase × V × I × PF / 1000I = P × 1000 / (Fphase × V × PF)where:
- I
- Calculated current[A]
- P
- Active power[kW]
- V
- System voltage[V]
- PF
- Power factor for AC systems
- S
- Apparent power[kVA]
- Fphase
- 1 for DC or single-phase; √3 for three-phase
Use equipment nameplate current when available, especially for nonlinear loads, motor loads, or equipment with high starting current.
How to convert kW, kVA, and amps
Choose the value you have and the value you need. Current conversions require voltage and system type; direct kW and kVA conversions require only power and power factor.
- Choose one of the five conversion modes.
- Select the system only for current conversions; kW and kVA conversion is for AC power.
- Enter power or current, and voltage only when it is shown.
- Enter power factor for active-power AC conversions.
- Review the result and formula basis before equipment selection.
Convert kW to kVA or kVA to kW
For AC electrical input power, divide kW by power factor to find kVA, or multiply kVA by power factor to find kW. At PF = 0.8, 100 kW equals 125 kVA and 100 kVA equals 80 kW. Voltage and phase do not change this power relationship. Use a power factor greater than zero and no greater than one.
100 kW / 0.8 = 125 kVA
100 kVA × 0.8 = 80 kW
kW to amps calculation example
A 15 kW balanced three-phase load at 400 V and 0.90 power factor draws approximately 24.1 A.
I = 15,000 / (√3 × 400 × 0.90) = 24.1 A
| Input or result | Value |
|---|---|
| Electrical input power | 15 kW |
| Voltage | 400 V three-phase |
| Power factor | 0.90 |
| Apparent power | 16.7 kVA |
| Line current | 24.1 A |
kW vs. kVA
Kilowatts measure active power, while kilovolt-amperes measure apparent power. For an AC load, kW equals kVA multiplied by power factor. Equipment efficiency belongs in motor or generator output calculations, not this direct electrical conversion.
| Quantity | Meaning | Typical use |
|---|---|---|
| kW | Real power | Useful output or electrical energy converted to work and heat |
| kVA | Apparent power | Transformer, generator, and system loading |
| A | Current | Cable, breaker, contactor, and busbar planning |
Single-phase vs. three-phase current conversion
Single-phase current uses voltage directly in the denominator. Balanced three-phase current uses line-to-line voltage and the √3 factor. DC conversion does not use AC power factor.
Use nameplate current for final equipment selection
Calculated current is an estimate for balanced steady-state conditions. Motors, transformers, rectifiers, variable-speed drives, chargers, and nonlinear loads may have starting current, harmonics, duty cycles, or manufacturer ratings that control final selection.
Three Phase Current CalculatorMotor Current CalculatorCircuit Breaker Size Calculator
Assumptions
- Balanced three-phase load
- Three-phase voltage is line-to-line
- Power factor applies to active-power AC conversions
Important Warnings
- Use nameplate data when available.
- Nonlinear loads, harmonics, and starting current are not included.