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Use this calculator to

  • Size the current draw of a 400 V three-phase supply from its kVA rating before ordering switchgear
  • Check whether a 230 V single-phase circuit can carry a load quoted in kVA
  • Translate your agreed supply capacity (ASC) in kVA into the maximum current your site can pull
  • Compare generator or UPS kVA ratings against cable and breaker ratings in amps

kVA to Amps Calculator

Supply phase

Common supply sizes (kVA)

Standard UK transformer and generator ratings. Selecting one fills the kVA input.

Current

Enter an apparent power above zero kVA to see the current.

Common kVA ratings at the selected voltage and phase

Computed at 230 V, single-phase.

Rating (kVA)Current (A)
50217.4
100434.8
200869.6
3151,370
5002,174
8003,478
1,0004,348
2,0008,696

For business

Why this matters for businesses

Most UK commercial sites are quoted incoming supply in kVA, sized in amps per phase, and billed in kWh, and the three numbers have to line up. A 500 kVA supply at 400 V three-phase works out to roughly 722 amps per phase, and that figure sets the upper limit on every cable, breaker, busbar, and submeter downstream of the cut-out. Get the conversion wrong by 10 percent and the difference shows up either as nuisance tripping or as paid-for capacity that the site never uses.

Maximum Import Capacity (MIC) bands are where this gets expensive. A site that creeps above its agreed MIC pays excess capacity charges that can run to several thousand pounds a year on a single MPAN, and the fix is either to lift the MIC (and pay more in standing charges every month) or to actively manage demand to stay under it. Picking the right band depends on understanding the kVA-to-amps relationship for the actual load mix on site, not just the nameplate sum.

Purely Energy works with clients on MIC reviews where a careful audit can drop the agreed capacity by 20 to 30 percent without restricting operations, or alternatively flag where an EV charger rollout or a heat-pump retrofit needs a capacity uplift booked with the DNO well in advance. The half-hourly data tells the truth on actual draw, and the conversion maths here is how that data becomes a defensible procurement decision.

Common questions

How do I convert kVA to amps?

For single-phase: amps = kVA x 1,000 / volts. For three-phase: amps = kVA x 1,000 / (volts x 1.732), where 1.732 is the square root of three and the voltage is line-to-line. On UK supplies that means 1 kVA draws about 4.3 A at 230 V single-phase, or about 1.4 A at 400 V three-phase. Pick single or three phase in the calculator and it applies the right formula.

How many amps is a 100 kVA three-phase supply at 400 V?

About 144 A per phase: 100,000 / (400 x 1.732) = 144.3 A. The arithmetic scales linearly, so a 200 kVA supply gives roughly 289 A and a 500 kVA supply roughly 722 A at 400 V. These per-phase figures are what your switchgear, cabling and main breaker need to be rated to carry continuously.

Why is supply capacity quoted in kVA rather than amps or kW?

Distribution network operators (DNOs) set your agreed supply capacity (ASC, sometimes called maximum import capacity or MIC) in kVA because their cables and transformers are limited by current and voltage, which is apparent power, not by the real power your equipment usefully consumes. Two sites drawing the same kW can stress the network differently if their power factors differ, so the DNO charges for the kVA it must reserve.

What is the difference between line voltage and phase voltage?

On a UK three-phase supply the line-to-line voltage is 400 V and the line-to-neutral (phase) voltage is 230 V; the two differ by the square root of three. The three-phase formula in this calculator expects the 400 V line voltage. If you enter 230 V in the three-phase calculation you will overstate the current by about 73 percent.

What happens if my site exceeds its agreed supply capacity?

For half-hourly metered sites, exceeding your ASC triggers excess capacity charges under DCP161, billed on the kVA you took above the agreed level, and persistent breaches can also overload the DNO connection itself. The fix is either to reduce peak demand or to apply to the DNO for a higher ASC. Converting your ASC to amps with this calculator is a quick first check on how close your peak current runs to the limit.

Do I need power factor to convert kVA to amps?

No. kVA is apparent power, which already combines real and reactive power, so the current follows directly from kVA and voltage. Power factor only enters when you start from kW: in that case convert kW to kVA first by dividing by power factor, or use the kW to amps calculator, which takes power factor as an input.

Related calculators

The conversions that procurement and engineering use alongside this one.

kVA to Amps Calculator | Free UK Tool | Purely Energy