Power Factor Calculator

What this calculator does

The Power Factor Calculator provides fast estimates using standard electrical relationships. Enter Real Power (P), Apparent Power (S) to compute results for real-world electrical scenarios. Use it for quick checks, comparisons, and documentation while planning.

Inputs explained

  • Real Power (P): Power value as labeled (W, kW, VA, or kVA).
  • Apparent Power (S): Power value as labeled (W, kW, VA, or kVA).

How it works / Method

The calculator applies the listed formulas to the values you enter and then formats the result in standard units. For AC calculations, power factor and phase selection adjust real power to match typical loads.

Formulas used

  • PF = P / S
  • PF = cos(θ)

Units: P in watts (W)

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Power Factor Calculator

Calculate power factor (PF)

W
VA
Result
—

Formula

PFPF = P ÷ S
AlsoPF = cos(θ)

Power Factor ranges from 0 to 1

Typical Power Factors

Load Type PF
Resistive (heaters) 1.0
Fluorescent lights 0.9-0.95
Induction motors 0.7-0.85
Unloaded motors 0.2-0.3

Related

kW to kVAkVA to kW

Step-by-step example

Scenario: A motor draws 8 kW real power and 10 kVA apparent power.

Formula: PF = kW / kVA

  1. PF = 8 / 10
  2. PF = 0.8 (or 80%)

Result: 0.8 power factor

Use cases

  • Estimate real power from apparent power and power factor.
  • Compare motor or transformer efficiency assumptions.
  • Cross-check utility bill kW vs kVA relationships.
  • Evaluate the impact of power factor on system sizing.

Assumptions & limitations

  • Results are estimates and may be rounded; small differences are expected.
  • Inputs assume steady-state values; transient and surge effects are not modeled.
  • Voltage can vary by supply, load, and location; use measured values when possible.
  • Power factor varies by load type; use a realistic value for inductive equipment.
  • Wiring rules and safety codes vary by jurisdiction; consult a licensed electrician for installation decisions.

Sources & references

Related calculators

Frequently Asked Questions

The Power Factor Calculator estimates real power, apparent power, or power factor. It helps you understand inductive load behavior. You can compare kW and kVA under different PF values. Use it to explore efficiency and sizing impacts. Results are idealized and for planning only. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

Low power factor increases current for the same real power. That can increase losses and voltage drop. Utilities may apply penalties for poor PF. Understanding PF helps estimate kW from kVA. Use measured PF values when available. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

Resistive loads are close to PF = 1.0. Motors and transformers are often 0.7 to 0.95. Use the equipment nameplate or a power meter. If unsure, choose a conservative value. Document assumptions for later review. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

Yes, when the calculator includes a three-phase option. Use line-to-line voltage for most three-phase systems. Confirm whether current is line or phase value. The sqrt(3) factor is applied for three-phase power. Check your system configuration before interpreting results. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

Accuracy depends on the input PF, voltage, and current. PF can change with load and operating conditions. Voltage can vary across the day. Use measured values when possible. Treat the output as an estimate for planning. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

Use it for preliminary sizing and understanding only. Final selection should follow manufacturer data. Apply local electrical code requirements. Consider inrush current and efficiency separately. Consult a licensed professional for installations. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.