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.
Tips
- Keep track of signs of charges – like charges repel, unlike attract.
- Use SI units (C, V, A, T) in the formulas; the menus convert prefixes.
- Vacuum permittivity ε₀ = 8.854 × 10⁻¹² F/m and permeability μ₀ = 4π × 10⁻⁷ H/m.
- For AC power, include the power factor.
Common mistakes to avoid
- Using microcoulombs as coulombs.
- Forgetting the √3 factor in three-phase power.
- Mixing RMS and peak values.
Inputs explained
| Field | What to enter |
|---|---|
| Known values | Choose one: Real and apparent power, Voltage, current and real power, Resistance and reactance |
| Real power P | Units: kW, W |
| Apparent power S | Units: kVA, VA |
| Voltage V | Units: V, kV, mV |
| Current I | Units: A, mA, µA, kA |
| Resistance R | Units: Ω, kΩ, MΩ, mΩ |
| Reactance X | Units: 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 factor |
|---|---|
| 4 | 0.4 |
| 6 | 0.6 |
| 8 | 0.8 |
| 10 | 1 |
| 12 | 1.2 |
| 16 | 1.6 |
Formula
PF = P/S = cos φ = R/|Z|, Q = √(S² − P²), |Z| = √(R² + X²)
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).
Frequently asked questions
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.
What formula does the Power Factor Calculator use?
PF = P/S = cos φ = R/|Z|, Q = √(S² − P²), |Z| = √(R² + X²).