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Free calculator

Use this calculator to

  • Size a UPS from the current its connected equipment draws
  • Convert circuit current into VA for transformer and inverter ratings
  • Check small power loads against the VA rating on a nameplate
  • Compare DC, single-phase and three-phase apparent power for the same current

Amps to VA Calculator

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

A
V
Result
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A
V
PF
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A
V
PF
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Formulas

  • DC / AC Single-Phase: VA = A × V
  • AC Three-Phase: VA = A × V × √3

Related Calculators

VA→A

VA to Amps

Convert volt-amps to current (A)

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A→kVA

Amps to kVA

Convert current (A) to apparent power (kVA)

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A→kW

Amps to kW

Convert current (A) to real power (kW)

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Common scenarios

Select one to run it in the calculator above.

For business

Why this matters for businesses

UPS, inverter and small-transformer ratings are quoted in VA or kVA because the equipment has to size for apparent power, not real load. For a comms room or small data hall the inrush, the power factor of mixed IT and HVAC loads, and the diversity factor across racks all sit between the amps you measure and the VA you actually need to specify. A 20 A circuit at 230 V is 4,600 VA on paper, but a UPS sized to that headline figure may be running closer to its limit than the design intended.

Resilience capex tends to be specified in a hurry after a near-miss. The temptation is to round up aggressively, which is fine for capital but expensive for the standing draw and battery replacement cycle that follows. Sizing UPS to actual demand plus a deliberate margin (rather than a 2x safety factor) keeps the running cost and the maintenance schedule under control, and the amps-to-VA conversion is where that conversation starts.

Purely Energy supports facilities and IT teams reviewing comms infrastructure, particularly across multi-site retail, hospitality and commercial property estates where the same UPS pattern repeats across dozens of sites. Half-hourly metering through Purely Insights highlights where standby load runs higher than the design assumed, which is usually the first sign that the original VA sizing was generous, and gives the procurement team a defensible figure to take into the next refresh cycle.

Common questions

How do I convert amps to VA?

For DC and single-phase AC, multiply current by voltage: VA = A x V, so 10 A at 230 V is 2,300 VA. For three-phase, multiply by the square root of 3 as well: VA = A x V x 1.732, using the 400 V line voltage. The result is apparent power, the figure transformers and UPS units are rated in.

What is the difference between VA and watts?

VA is apparent power, the total voltage times current flowing in the circuit. Watts are real power, the portion doing useful work: W = VA x power factor. For a resistive heater they are equal, but for IT equipment, motors and anything with a switched-mode supply the wattage is lower than the VA, so sizing by watts alone under-specifies the supply.

Why are UPS systems rated in VA rather than watts?

A UPS has to carry the full current of its load, including the reactive component that does no useful work, so its inverter and transformer are limited by apparent power. Most UPS units state both a VA and a watt rating, and you must stay inside both. Convert your load current to VA first, then check the watt rating against the real power.

Why does the power factor field not change the VA result?

Apparent power is voltage times current by definition, so power factor does not enter the calculation. Power factor only matters when converting VA into real watts (W = VA x PF) or working back from watts to the VA a supply must carry. The field is there so you can keep your load's nameplate figures together while you work.

When should I use VA and when kVA?

They are the same quantity at different scales: 1 kVA equals 1,000 VA. Small equipment such as desktop UPS units, doorbell transformers and control gear is usually rated in VA, while building supplies, generators and distribution transformers are rated in kVA. Divide a VA figure by 1,000 to compare it against a supply capacity quoted in kVA.

Related calculators

The conversions that procurement and engineering use alongside this one.

Amps to VA Calculator | Free UK Tool | Purely Energy