About the Three-Phase Power Calculator
This three-phase power calculator converts between real power (kW), apparent power (kVA), line current (amps) and voltage for balanced three-phase systems. Pick what you know — kW, kVA or amps — enter the voltage and power factor, and it returns the current per line, kW, kVA, kVAR and the equivalent horsepower.
It is built for electricians sizing feeders and breakers, engineers checking motor and heater loads, and facility managers reading utility or panel data. You can enter line-to-line voltage (the usual nameplate figure such as 208, 400 or 480 V) or line-to-neutral voltage (such as 120, 230 or 277 V) and the calculator handles the √3 factor for you.
The formulas assume a balanced load — the same current in all three phases — and sinusoidal waveforms. Motor nameplates list output (shaft) power, so for a motor divide by its efficiency to get the electrical input kW before converting to amps. If the power factor is left blank or 0, a kW input cannot be converted and the current shows “—”. Horsepower uses 1 hp = 745.7 W (the 550 ft·lbf/s mechanical horsepower). For conductor and breaker sizing, apply your electrical code’s rules to the result.
With the default inputs, the line current is 70.75 A. Change any value above to recalculate instantly.
How to use the three-phase power calculator
- 1Choose which quantity you know: kW, kVA or amps.
- 2Enter that value and the system voltage.
- 3Say whether the voltage is line-to-line or line-to-neutral.
- 4Enter the power factor (use 1.0 for resistive loads).
- 5Read the line current, kW, kVA and kVAR, and compare other voltages in the table.
Formula and method
In a balanced three-phase system the total apparent power is √3 times the line-to-line voltage times the line current. Real power is apparent power multiplied by the power factor, and reactive power is apparent power × √(1 − PF²). Rearranging gives the current for a known kW or kVA.
If you enter line-to-neutral (phase) voltage, the calculator converts it with V_LL = √3 × V_LN, which is the same as P = 3 × V_LN × I × PF. Horsepower is kW ÷ 0.7457. Results describe electrical input; for motors, divide shaft kW by efficiency first.
- V_LL
- Line-to-line voltage
- V_LN
- Line-to-neutral voltage (V_LL ÷ √3)
- I
- Line current in amps
- PF
- Power factor (cos φ)
- √3
- ≈ 1.732
Worked examples
50 kW load at 480 V, 0.85 power factor
Apparent power is 50 ÷ 0.85 = 58.82 kVA. Current = 58,824 ÷ (1.732 × 480) ≈ 70.8 A per line. The reactive power is 58.82 × √(1 − 0.85²) ≈ 31.0 kVAR.
100 A at 400 V, power factor 0.9
Apparent power = 1.732 × 400 × 100 ÷ 1000 = 69.28 kVA. Multiplying by the 0.9 power factor gives 62.35 kW of real power, about 83.6 hp.
30 kW heater on 230 V line-to-neutral
A 230 V phase voltage corresponds to 230 × 1.732 ≈ 398 V line-to-line. With a resistive load (PF 1), each line carries 30,000 ÷ (3 × 230) ≈ 43.5 A.
50 kW with the power factor left at 0
kVA = kW ÷ PF is undefined when PF is 0, so the calculator shows “—” for current and kVA instead of a misleading 0 A and asks for a power factor between 0.01 and 1.
Frequently asked questions
How do I convert kW to amps in three-phase?+
Divide kW × 1000 by (1.732 × line-to-line voltage × power factor). For example, 50 kW at 480 V with a 0.85 power factor draws 50,000 ÷ (1.732 × 480 × 0.85) ≈ 70.8 A.
What is the three-phase power formula?+
P = √3 × V_LL × I × PF, where V_LL is the line-to-line voltage, I the line current and PF the power factor. Using phase voltage instead, P = 3 × V_LN × I × PF.
Why multiply by 1.732 (√3) in three-phase?+
The three phases are 120° apart, so the line-to-line voltage is √3 times the phase voltage. Combining the three phase powers gives a total of √3 × V_LL × I for a balanced load.
How many amps is a 10 hp three-phase motor at 480 V?+
Roughly 14 A. NEC Table 430.250 lists 14 A full-load current for a 10 hp, 460 V motor, which already allows for typical efficiency and power factor; always use the table or nameplate for sizing.
What is the difference between kW and kVA?+
kW is real power that does work; kVA is total apparent power including the reactive part that magnetizes motors and transformers. kW = kVA × power factor.