Guidance only — always verify against current standards and manufacturer instructions.
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This converter changes power in kilowatts into current in amps — and back again — for UK 230V single-phase and 400V three-phase supplies, with power factor taken into account. Electricians use it constantly: turning an appliance's kW rating into the design current for a circuit, or a measured current into the load in kW.
For single phase the tool divides the power by the voltage and power factor; for three phase it uses the line voltage with the √3 factor that accounts for the three-phase relationship. Enter the value, choose the direction and supply, set the power factor (1 for resistive loads such as heaters), and read off the result.
1φ: I = (kW × 1000) / (230 × pf) 3φ: I = (kW × 1000) / (√3 × 400 × pf)
I is the current in amps and kW × 1000 converts the power to watts. For single phase, the divisor is the 230V supply voltage multiplied by the power factor (pf). For three phase, the divisor is √3 (about 1.732) times the 400V line voltage times the power factor, which gives the current per line for a balanced load. Power factor is 1 for purely resistive loads such as heaters and showers, and less than 1 for motors and similar loads — a lower power factor means more current for the same useful power. The A → kW direction simply inverts the same equations.
Select kW → A to find the current a load draws, or A → kW to convert a measured current into power.
Pick single phase (230V) or three phase (400V). Three-phase results are the current per line for a balanced load.
Type in the kW or amps figure and the power factor — leave it at 1 for resistive loads like showers and heaters, or use the nameplate power factor for motors.
The conversion assumes the UK nominal voltages of 230V single phase and 400V three phase, and a balanced load across phases for three-phase calculations. Real supply voltage varies within tolerance, so measured currents will differ slightly from calculated ones.
Power factor matters for anything with windings or electronics. A 5.5kW motor at a power factor of 0.85 draws around 9.3A per phase on a 400V supply, not the 7.9A a unity calculation gives — undersizing on that difference is a classic error. Appliance nameplates usually state full-load current; where they do, prefer the nameplate figure.
The current from this conversion is the starting point for circuit design, not the end of it: the design current feeds into device selection, cable sizing with correction factors and voltage drop checks.
For a resistive load at power factor 1: 9500 / 230 ≈ 41.3A. That is the arithmetic behind a 9.5kW shower needing a 40A or 45A circuit — and why the cable and device must be sized for the shower's actual rating at nominal voltage.
Divide the power in watts by √3 × 400 × power factor. For example, 15kW at unity power factor on a 400V three-phase supply draws 15000 / (1.732 × 400) ≈ 21.7A per line. At a power factor of 0.8 the same output needs about 27A per line.
Use 1 for resistive loads — showers, immersion heaters, radiant heating. Motors typically run between 0.8 and 0.9 at full load, and the nameplate value is the one to use where available. A lower power factor means more current for the same kW, so guessing high on pf undersizes the circuit.
The calculated figure is the line current — the current flowing in each of the three line conductors for a balanced load. It is not divided by three or summed across phases; each phase conductor and its protective device sees that current.
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