Power and current calculator
Convert between kW and amps for single or three phase, including power factor.
A
V
Line-to-neutral voltage (230 V in the UK).
1 for heaters and other resistive loads. Motors are often 0.8 to 0.9; check the rating plate.
Current
–A
Apparent power–
Per phase–
The formulas
Single phase: I = P ÷ (V × pf)
Three phase: I = P ÷ (√3 × VL × pf)
For three phase, VL is the line-to-line voltage, 400 V on a standard UK supply. The result is the current in each line of a balanced load.
Worked examples
A 7.2 kW car charger on 230 V single phase at power factor 1 draws 7200 ÷ 230 = 31.3 A.
A 15 kW three-phase motor at power factor 0.85 on 400 V draws 15000 ÷ (1.732 × 400 × 0.85) = 25.5 A per line. Starting current is much higher, so check the manufacturer's data when choosing protection.