kVA calculator
These figures come straight from the voltage and current you enter. They do not account for power factor, harmonics or diversity, and they are not a service or feeder sizing — treat the kVA as a starting point and defer to the equipment nameplate, your code book and your authority having jurisdiction.
Enter the voltage and current and the tool gives the apparent power in kVA, or flip it to find the current a given kVA draws at your voltage. The single-phase and three-phase forms differ only by the √3 factor, which the phase switch handles.
Worked example
A three-phase load at 480 V drawing 100 A is √3 × 480 × 100 ÷ 1,000 ≈ 83.1 kVA. Going the other way, a 50 kVA three-phase load at 480 V pulls 50,000 ÷ (√3 × 480) ≈ 60.1 A per line. The same 100 A on a single-phase 240 V supply would be only 240 × 100 ÷ 1,000 = 24 kVA.
The formula
single phase: kVA = V × A ÷ 1000 · three phase: kVA = √3 × V × A ÷ 1000
Apparent power is simply the product of voltage and current, scaled to kilovolt-amps by dividing by a thousand. Three-phase power adds the √3 (about 1.732) that comes from the geometry of three line voltages 120° apart, using the line-to-line voltage.
Questions
- How do I calculate kVA?
- For a single-phase supply, kVA is volts times amps divided by 1,000. For three-phase, multiply by the square root of three as well: kVA = √3 × volts × amps ÷ 1,000. Enter the voltage and current here, pick the phase, and the tool returns the apparent power in kVA.
- How do I find amps from kVA?
- Rearrange the same formula. Single phase: amps = kVA × 1,000 ÷ volts. Three phase: amps = kVA × 1,000 ÷ (√3 × volts). Flip the tool to solve for current and it does exactly that, which is the usual question when you are sizing a feed from a transformer rating.
- What is the difference between kVA and kW?
- kVA is apparent power — the full product of volts and amps. kW is real power, the part that does work. They are linked by the power factor: kW = kVA × power factor. On a purely resistive load the two are equal; on motors and other inductive loads the power factor is below one, so the kW is less than the kVA.
- Which voltage do I use for three phase?
- Use the line-to-line voltage — 208, 480 or 600 in common systems — because the √3 formula is written around it. Entering a phase-to-neutral voltage by mistake is the most common error here, and it throws the result off by a factor of √3.
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