# Power Factor Calculator

URL: https://speedycalculator.com/calculators/physics/power-factor/
Last updated: 2026-10-30

> The power factor calculator finds the power factor, phase angle and reactive power of an AC load from its real and apparent power, from voltage, current and real power, or from its resistance and reactance.

## Inputs

- Known values
- Real power P (kW, W)
- Apparent power S (kVA, VA)
- Voltage V (V, kV, mV)
- Current I (A, mA, µA, kA)
- Resistance R (Ω, kΩ, MΩ, mΩ)
- Reactance X (Ω, kΩ, MΩ, mΩ)

## Results

- Power factor
- Phase angle φ
- Apparent power
- Reactive power
- Impedance |Z|

## Formula

```
PF = P/S = cos φ = R/|Z|,  Q = √(S² − P²),  |Z| = √(R² + X²)
```

## Explanation

Power factor shows how effectively a load uses the current it draws. Inductive loads like motors have a lagging power factor; utilities may charge large customers for poor PF, which is corrected with capacitor banks.

### How to use the Power Factor Calculator

- **Known values**
- **Real power P**
- **Apparent power S**
- **Voltage V**
- **Current I**
- **Resistance R**
- **Reactance X**

Results update as you type, every field has its own unit menu, and everything is calculated in your browser.

### How it works

Choose what you know and enter the values.

### Inputs explained

FieldWhat to enterKnown valuesChoose one: Real and apparent power, Voltage, current and real power, Resistance and reactanceReal power PUnits: kW, WApparent power SUnits: kVA, VAVoltage VUnits: V, kV, mVCurrent IUnits: A, mA, µA, kAResistance RUnits: Ω, kΩ, MΩ, mΩReactance XUnits: Ω, kΩ, MΩ, mΩ

### What each result means

- **Phase angle φ** = deg(acos([Power factor]))
- **Reactive power** = [Apparent power]×sin(acos([Power factor]))
- **Impedance |Z|** = sqrt([Resistance R]^2 + [Reactance X]^2)

### Example values

How the main result changes when **Real power P** changes and everything else stays at the example values above:

Real power P (kW)Power factor40.460.680.8101121.2161.6

## Worked example

Inputs — Known values: Real and apparent power; Real power P: 8 kW; Apparent power S: 10 kVA.

Results — **Power factor = 0.8**; Phase angle φ = 36.8699 °; Apparent power = 10,000 VA; Reactive power = 6,000 VAR.

## Key terms

- **Reactive power**: Power that oscillates between source and load (VAR).

## FAQ

**What is a good power factor?**
Above 0.95 is generally considered good.

**What causes low power factor?**
Inductive loads such as motors and transformers.

**How is power factor corrected?**
With capacitors that supply reactive power locally.

**What is leading vs lagging?**
Capacitive loads lead; inductive loads lag.


## Sources

- [OpenStax – University Physics Volume 2](https://openstax.org/details/books/university-physics-volume-2)
- [The Engineering ToolBox](https://www.engineeringtoolbox.com/)