About the Amps to VA Calculator
This calculator turns a current in amps into apparent power in volt-amps (VA), the figure used to size UPS units, transformers, generators and inverters. Apparent power is simply voltage times current, with an extra √3 for three-phase supplies measured between two lines. It does not use the power factor, because VA counts all the current a load draws, including the part that does no useful work. Enter the amps and the voltage, choose the supply, and the VA and kVA appear straight away. Everything is worked out in your browser.
Updated October 2026
How to use the Amps to VA Calculator
- 1Choose DC, single-phase AC or three-phase AC.
- 2Type the current in amps.
- 3Type the voltage. For three-phase, use the voltage between two lines, such as 400 V or 480 V.
- 4Read the apparent power in VA and kVA.
- 5Press Copy result to paste it into a quote, a note or a spreadsheet.
When volt-amps matter more than watts
UPS units, transformers, generators and inverters are rated in VA or kVA because their limit is the current they can carry, not the useful power the load turns into heat, light or motion. A motor with a poor power factor draws more current than its watt rating suggests, so a generator sized on watts alone may trip. Converting the measured or rated current to VA tells you the load the equipment really sees.
How the amps to VA formula works
For direct current and single-phase AC the apparent power is the product of current and voltage. Three-phase supplies carry three currents, and when the voltage is measured between two lines the total becomes √3 times the single product.
Example: a workshop compressor draws 12 A on a 400 V three-phase supply. VA = 1.732 × 12 × 400 ≈ 8,314 VA, or 8.3 kVA.
- DC and single-phase: VA = A × V
- Three-phase: VA = √3 × A × V (line-to-line)
- kVA = VA ÷ 1,000
Tips for accurate figures
Use the running current from a clamp meter or the rating plate, not the fuse rating. Motors also draw a brief starting current several times higher, so leave extra headroom when you size a generator for them. For mixed loads, convert each one and add the VA together; that sum is the safe figure to compare with a UPS or inverter rating.
Using it on a phone or computer
The boxes are large enough to tap on a phone at a fuse board or a job site, and the result updates as you type. On a computer, change one value and watch the VA move, which is handy when you compare 230 V and 400 V options. Nothing you type leaves the page. Apparent power in VA is what a UPS or transformer label shows. Go the other way with the VA to Amps Calculator, move up to larger loads with the kVA to Amps Calculator, and find the real power in watts with the Amps to Watts Calculator.
Features
- Amps to VA and kVA in one step
- DC, single-phase and three-phase
- Uses the line-to-line voltage for three-phase
- Clear error messages for impossible values
- Copy the answer with one tap
- Runs in your browser, nothing is uploaded
Frequently asked questions
How do I convert amps to VA?
Multiply the amps by the volts. For single-phase AC or DC, VA = A × V, so 10 A at 230 V is 2,300 VA. For three-phase, VA = √3 × A × V(line-to-line), so 10 A at 400 V is about 6,928 VA.
Is VA the same as watts?
Only when the power factor is 1, as with heaters and kettles. Watts are the real power that does work; VA is the apparent power the wiring has to carry. Watts = VA × power factor.
Why doesn't the calculator ask for the power factor?
Because volt-amps don't depend on it. A motor drawing 10 A at 230 V loads the supply with 2,300 VA whatever its power factor; the power factor only decides how many of those VA become watts.
How many VA is 1 amp?
At 120 V, 1 A is 120 VA. At 230 V it is 230 VA. In three-phase at 400 V it is about 693 VA, because of the √3 factor.
How do I size a UPS from amps?
Add up the current of everything the UPS will power, convert it to VA with this calculator, then pick a UPS rated 20 to 30% above that figure so it isn't running flat out.
What voltage should I use for three-phase?
Use the line-to-line voltage, the one measured between two phases, such as 400 V in Europe or 480 V in North American industry. Using the phase-to-neutral voltage here would give a figure that is too low by √3.