Calculate apparent power in VA or kVA from voltage and current, real and reactive power, or real power and power factor for single- or three-phase loads.
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Apparent Power Formula
The calculator uses sinusoidal AC power relationships. Choose apparent power from voltage/current, real/reactive power, real power/power factor, or voltage/impedance; other modes calculate current, real/reactive power from S and PF, or PF from real/apparent power. Three-phase voltage/current results assume a balanced load.
- 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 = โ(Pยฒ + Qยฒ).
The rearrangement P = โ(Sยฒ – Qยฒ) is included above for reference. To calculate real power in this widget, choose the S-and-PF mode.
In the power-factor mode, apparent power and real power also give reactive-power magnitude using |Q| = โ(Sยฒ – Pยฒ). Its sign requires knowing whether the load is inductive or capacitive.
The calculator converts all inputs to base units before calculating: W for true power, VAR for reactive power, and VA for apparent power. It reports apparent power in kVA and VA, real power in kW and W, and reactive power in kVAR and VAR.
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.
The apparent power is 10 kVA.
Example 2: Calculate reactive power
You have 25 kVA of apparent power and 20 kW of true power. Select the power-factor mode to obtain PF = 0.8 and the reactive-power magnitude below.
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.
