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Free calculator

Use this calculator to

  • Translate a measured or fused current into the kVA a supply must carry
  • Check a site's running load against its Agreed Supply Capacity (ASC) in kVA
  • Size a generator, transformer or UPS from the current it has to serve
  • Compare single-phase and three-phase capacity for the same current

Amps to kVA Calculator

Convert current (A) to apparent power (kVA).

A
V
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A
V
PF
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A
V
PF
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Formulas

  • DC / AC Single-Phase: kVA = (A × V) / 1000
  • AC Three-Phase: kVA = (A × V × √3) / 1000

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Amps to VA

Convert current (A) to volt-amps (VA)

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Common scenarios

Select one to run it in the calculator above.

For business

Why this matters for businesses

kVA is the unit your DNO and supplier care about on the contract, but operations teams usually live in amps day to day on the floor. The conversion sits behind every Authorised Supply Capacity (ASC), Maximum Import Capacity (MIC) and Maximum Export Capacity (MEC) decision, every transformer specification, and every generator sizing exercise on a commercial or industrial site. Get the conversion wrong at design stage and the site either chokes at peak demand or pays for headroom on the bill that never gets used in production.

Availability Charges scale linearly with the kVA you have agreed with the DNO, and they bill every month whether you draw the capacity or not. On a 1,000 kVA HV connection a 20% over-spec can mean four to five figures per year of waste, year after year, against an actual peak that never gets close. Reviewing kVA against measured half-hourly demand is one of the highest-return exercises an energy manager can run.

Purely Energy reviews MIC, MEC and capacity bands for portfolio clients as standard practice. We pull twelve months of HH data, plot demand against agreed capacity, and where there is genuine headroom we manage the DNO process to right-size the contract end-to-end. The calculator is the engineering check; the application and the contract change are where the bill actually moves, and for a multi-site business that exercise often pays back in a single quarter once a few sites are right-sized together.

Common questions

How do I convert amps to kVA on a three-phase supply?

Use kVA = A x V x 1.732 / 1000, where 1.732 is the square root of 3 and V is the line-to-line voltage, 400 V in the UK. So 100 A per phase at 400 V is 100 x 400 x 1.732 / 1000, about 69.3 kVA. Use the highest phase current if the load is unbalanced.

How do I convert amps to kVA on a single-phase supply?

For single-phase the formula is kVA = A x V / 1000. A 100 A supply at 230 V can carry 23 kVA. Power factor does not appear in this calculation: kVA is apparent power, set purely by voltage and current. Power factor only matters when you convert kVA into the real kW the load delivers.

What is the difference between kVA and kW?

kVA is apparent power, the total voltage times current a supply must carry. kW is real power, the part that does useful work: kW = kVA x power factor. Cables, transformers and generators are rated in kVA because conductors heat up with the full current regardless of power factor, so a poor power factor wastes supply capacity.

Why does my electricity supply capacity get quoted in kVA?

Half-hourly metered sites in the UK have an Agreed Supply Capacity, sometimes called the Maximum Import Capacity, set in kVA with the distribution network operator. The network has to be sized for the current you draw, not just the useful power, so capacity is reserved and charged in kVA. Converting your maximum current into kVA shows how close you run to that limit.

What voltage should I enter for a UK supply?

Enter 230 V for single-phase and 400 V for three-phase, which are the UK nominal voltages at 50 Hz. The three-phase figure is the line-to-line voltage, and the formula's square root of 3 accounts for the phase relationship. Actual voltage is permitted to vary within statutory limits, so measured values may differ slightly from nominal.

Related calculators

The conversions that procurement and engineering use alongside this one.

Amps to kVA Calculator | Free UK Tool | Purely Energy