Apparent Power Calculator - Calculator Academy

Calculate apparent, true, or reactive power from any two known values in W, VAR, and VA for electrical circuits with unit conversions.

Apparent Power Formula

The apparent power calculator uses the power triangle relationship between true power, reactive power, and apparent power. Enter any two values to calculate the missing third value.

S = \sqrt{P^2 + Q^2}

P = \sqrt{S^2 - Q^2}

Q = \sqrt{S^2 - P^2}

S = apparent power, measured in VA, kVA, or MVA
P = true power, also called real power, measured in W, kW, or MW
Q = reactive power, measured in VAR, kVAR, or MVAR

If true power and reactive power are entered, the calculator finds apparent power using S = √(P² + Q²).

If apparent power and reactive power are entered, the calculator finds true power using P = √(S² – Q²).

If apparent power and true power are entered, the calculator finds reactive power using Q = √(S² – P²).

The calculator converts all inputs to base units before calculating: W for true power, VAR for reactive power, and VA for apparent power. It then converts the result back to the unit you selected.

Power Unit Conversions

Use these conversions when checking values manually or comparing results in different units.

Quantity	Base Unit	kilo Unit	mega Unit
True power	1 W	1 kW = 1,000 W	1 MW = 1,000,000 W
Reactive power	1 VAR	1 kVAR = 1,000 VAR	1 MVAR = 1,000,000 VAR
Apparent power	1 VA	1 kVA = 1,000 VA	1 MVA = 1,000,000 VA

Term	Meaning	Common Use
True power, P	Power that does useful work	Heating, lighting, mechanical output
Reactive power, Q	Power exchanged by inductive or capacitive loads	Motors, transformers, magnetic fields
Apparent power, S	Combined effect of true and reactive power	Sizing generators, transformers, and electrical equipment

Example Apparent Power Calculations

Example 1: Calculate apparent power

You have a load with 8 kW of true power and 6 kVAR of reactive power.

S = \sqrt{8^2 + 6^2}

S = \sqrt{64 + 36} = \sqrt{100} = 10

The apparent power is 10 kVA.

Example 2: Calculate reactive power

You have 25 kVA of apparent power and 20 kW of true power.

Q = \sqrt{25^2 - 20^2}

Q = \sqrt{625 - 400} = \sqrt{225} = 15

The reactive power is 15 kVAR.

Apparent Power Calculator FAQ

What is apparent power?

Apparent power is the total power demand placed on an AC electrical system. It combines true power, which performs useful work, and reactive power, which supports electric and magnetic fields in AC circuits. Apparent power is measured in volt-amperes, usually VA or kVA.

Why is apparent power higher than true power?

Apparent power is higher than true power when reactive power is present. In AC systems with motors, transformers, or other inductive loads, some power moves back and forth between the source and the load instead of being converted into useful work. That extra reactive component increases apparent power.

Can apparent power be less than true power?

No. In the power triangle relationship, apparent power is the hypotenuse, so it must be greater than or equal to true power and reactive power. If you enter an apparent power value that is smaller than true power or reactive power, the values are not physically valid for this calculation.