kVA Calculator
Calculate apparent power in kilovolt-amps (kVA) from voltage and current. Choose single-phase or three-phase, enter volts and amps, and get kVA instantly — the rating used to size transformers, generators, and UPS systems.
How to Calculate kVA
kVA (kilovolt-amps) is apparent power — voltage multiplied by current, divided by 1,000.For three-phase circuits, the line values are also multiplied by √3 (about 1.732) to account for the three conductors sharing the load.
Single-phase: kVA = V × A ÷ 1,000
Three-phase: kVA = 1.732 × V × A ÷ 1,000
Worked example (single-phase): A 240V single-phase feeder carrying 50 amps supplies 240 × 50 ÷ 1,000 = 12 kVA.
Worked example (three-phase): A 480V three-phase feeder carrying 100 amps supplies 1.732 × 480 × 100 ÷ 1,000 = 83.1 kVA. Notice that the same 100 amps at 208V three-phase would supply only 36 kVA — voltage matters as much as current.
Going the other direction — finding the current a given kVA rating can deliver — is the most common transformer sizing task. Use our kVA to amps calculator for that, or the transformer sizing calculator to pick a standard kVA rating from your load.
kVA vs kW vs kVAR: The Power Triangle
AC power has three components, and confusing them is one of the most common mistakes in electrical work:
- kVA (apparent power) — the total power flowing in the circuit: volts × amps. This is what determines conductor sizing, transformer ratings, and generator ratings, because heating in wires and windings depends on current regardless of what the load does with it.
- kW (real power) — the portion of apparent power converted into useful work (heat, light, motion). This is what utility meters bill for and what engines driving generators must actually produce.
- kVAR (reactive power) — power that shuttles back and forth between the source and the magnetic fields of motors, transformers, and ballasts (or the electric fields of capacitors). It does no useful work but still occupies capacity in the system.
The three form a right triangle — the power triangle— where kVA is the hypotenuse:
kVA² = kW² + kVAR²
Power factor: PF = kW ÷ kVA
Example: a motor load drawing 80 kW of real power and 60 kVAR of reactive power has an apparent power of √(80² + 60²) = 100 kVA, and a power factor of 80 ÷ 100 = 0.8.
When each matters: use kVA when sizing transformers, generators, UPS units, and feeders; use kW when calculating energy costs, fuel consumption, or heat output; watch kVAR (and power factor) when a utility applies low-power-factor penalties or when equipment runs hotter than its real-power load suggests. To convert between the two ratings, use our kW to kVA calculator.
Frequently Asked Questions
How do you calculate kVA?
For single-phase circuits, kVA = Volts × Amps ÷ 1,000. For three-phase circuits, kVA = 1.732 × Volts × Amps ÷ 1,000, where 1.732 is the square root of 3. For example, a single-phase 240V circuit carrying 50 amps is 12 kVA (240 × 50 ÷ 1,000), while a three-phase 480V circuit carrying 100 amps is 83.1 kVA (1.732 × 480 × 100 ÷ 1,000).
What is the difference between kW and kVA?
kVA is apparent power — the total power flowing in the circuit — while kW is real power, the portion actually converted into useful work. They are related by the power factor: kW = kVA × PF. A 100 kVA load with a power factor of 0.8 delivers only 80 kW of real power. For purely resistive loads (heaters, incandescent lighting) the power factor is 1.0 and kW equals kVA.
What is kVAR and the power triangle?
kVAR is reactive power — power that oscillates between the source and the magnetic or electric fields of inductive and capacitive loads without doing useful work. The power triangle relates all three quantities: kVA² = kW² + kVAR². kVA is the hypotenuse, kW is the horizontal leg, and kVAR is the vertical leg. For example, a load drawing 80 kW and 60 kVAR has an apparent power of 100 kVA.
Why are transformers and generators rated in kVA instead of kW?
Because the heating in a transformer or generator winding depends on current, not on the power factor of the load connected to it. The manufacturer has no way to know what power factor the load will have, so equipment is rated by the maximum apparent power (kVA) it can deliver without overheating. The real power (kW) you can actually get out depends on your load's power factor.
How many kVA is 100 amps?
It depends on the voltage and phase configuration. At 240V single-phase, 100 amps is 24 kVA (240 × 100 ÷ 1,000). At 208V three-phase, 100 amps is 36 kVA (1.732 × 208 × 100 ÷ 1,000). At 480V three-phase, 100 amps is 83.1 kVA (1.732 × 480 × 100 ÷ 1,000). Higher voltage means more kVA for the same current.
Is 1 kVA equal to 1 kW?
Only when the power factor is exactly 1.0, which occurs with purely resistive loads such as electric heaters. For typical mixed commercial loads with power factors of 0.8 to 0.95, 1 kVA delivers only 0.8 to 0.95 kW of real power. kVA is always greater than or equal to kW.
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