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Free calculator

Use this calculator to

  • Verify the supply voltage behind a load when you know its kW and the amps from a clamp meter
  • Check whether a circuit reading is consistent with a 230 V single-phase supply
  • Confirm 110 V site transformer circuits are delivering what the tools expect
  • Investigate voltage drop when a motor draws more current than its rating suggests

kW to Volts Calculator

Convert power (kW) to voltage (V) using current (A) and power factor.

kW
A
PF
Result
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Formulas

  • V = (kW × 1000) / (A × PF)

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Common scenarios

Select one to run it in the calculator above.

For business

Why this matters for businesses

Power, voltage and current are locked together by the supply topology, so a motor that nameplates at a given kW will draw a current that depends on whether it sees 230 V single-phase, 400 V three-phase, or a DC supply at some intermediate voltage. Working backward from kW and current to voltage is the check that catches the wrong supply assumption before a procurement order goes in for the wrong frame size, the wrong starter or the wrong cable.

For an engineering manager validating a motor or pump replacement, this conversion is the integrity check between the asset register, the supplier quotation and what is actually on the wall. A 22 kW pump on a 415 V three-phase supply pulls roughly 38 A at unity power factor. If the as-built cable was sized assuming 230 V single-phase, the installation will not pass a periodic inspection, and the discrepancy is far cheaper to find on a spreadsheet than during commissioning.

On long runs, the same calculation feeds the voltage drop assessment that determines whether you need a larger conductor, a local transformer tap change, or a different distribution route. BS 7671 sets the tolerated drop, and the only way to sense-check a contractor's claim that a cable is fit for purpose is to run the numbers yourself. For a finance lead signing off the capex, that independent check is what keeps a refit project on budget and out of rework.

Common questions

How do I calculate voltage from kW and amps?

Use V = kW x 1000 / (A x PF). The kilowatts convert to watts, then dividing by the current and power factor leaves the voltage. For example, a 2.3 kW heater drawing 10 A at unity power factor gives 2,300 / 10 = 230 V, the UK nominal single-phase supply. For motors and other inductive loads, include the power factor or the calculated voltage will come out too high.

Does this formula work for three-phase circuits?

This calculator uses the single-phase form. For a balanced three-phase load, the line-to-line voltage is V = kW x 1000 / (1.732 x A x PF), where 1.732 is the square root of 3 and A is the line current. If you apply the single-phase formula to three-phase readings, the result will be wrong by that factor. Use the dedicated 3-phase power calculator for 400 V supplies.

Is UK mains 230 V or 240 V?

The UK nominal voltage is 230 V single-phase with a permitted tolerance of plus 10 per cent and minus 6 per cent, which allows anything from about 216 V to 253 V. In practice many UK supplies still measure nearer 240 V because the network was built to the older standard. Equipment sold for the UK must work across the whole tolerance band, so a calculated figure between 220 and 250 V is normal.

Why does my calculated voltage not match the nominal supply?

Three common reasons. First, the power factor you assumed may be wrong: a motor at PF 0.85 treated as unity will show an inflated voltage. Second, the kW and amp readings may have been taken at different moments while the load varied. Third, real voltage drop along long cable runs means the voltage at the equipment genuinely is lower than at the origin of the circuit. Small differences of a few volts are entirely normal.

What happens to the current if the voltage drops?

For a fixed-power load, current rises as voltage falls, because I = kW x 1000 / (V x PF). A motor delivering the same mechanical output on a sagging supply pulls more amps, runs hotter and trips protection sooner. This is why undervoltage at the end of long circuits matters: the same 5 kW load that draws 25 A at 230 V needs about 26 A at 220 V.

Related calculators

The conversions that procurement and engineering use alongside this one.

kW to Volts Calculator | Purely Energy