Power Factor Calculator

What Is Power Factor?

Power factor describes the relationship between real power and apparent power in an AC electrical system.

A power factor of 1.00 means that real power and apparent power are equal. Lower power factor means that more current is required to deliver the same amount of real power.

Real, Reactive, and Apparent Power

AC electrical systems are commonly described using three related quantities.

• Real Power (kW) — power that performs useful work, such as turning a motor shaft or producing heat.
• Reactive Power (kVAR) — power associated with energy storage and return in inductive or capacitive equipment.
• Apparent Power (kVA) — the combined electrical loading represented by voltage and current.

3-Phase Power Factor Formula

For a balanced three-phase system using line-to-line voltage:

Combining these relationships gives:

Single-Phase Power Factor Formula

For a single-phase system:

Therefore:

Worked Example

Suppose a 480 V three-phase system is drawing 20 A and consuming 12 kW of real power.

The power factor is then:

The remaining apparent power is associated with reactive power in the system.

Why Power Factor Affects Current

For a given amount of real power, lower power factor requires more current.

In a three-phase system:

This is why power factor is important when evaluating conductor loading, transformer capacity, switchgear, motor operation, and electrical distribution systems.

Leading and Lagging Power Factor

Inductive loads such as motors and transformers commonly have lagging power factor because current lags voltage.

Capacitive loads can produce leading power factor because current leads voltage.

The calculator determines the magnitude of power factor from the supplied voltage, current, and real power. It does not determine whether the system is leading or lagging.

Power Factor and Motors

Motors are a common source of reactive power in industrial and commercial electrical systems.

Motor power factor varies with operating conditions, motor design, loading, and other factors. The power factor listed on a motor nameplate or obtained from an appropriate measurement should be used when available.

Power factor should not be confused with motor efficiency. Efficiency describes the relationship between mechanical output and electrical input power, while power factor describes the relationship between real and apparent electrical power.

Field Troubleshooting

If calculated power factor appears unexpectedly low, verify the measurements and system configuration before assuming the load itself is the problem.

1. Verify the voltage measurement and whether it is line-to-line or line-to-neutral.
2. Verify the current measurement and confirm the correct phase or system measurement.
3. Confirm that real power is measured in kW rather than kVA.
4. Confirm whether the system is single-phase or three-phase.
5. Compare calculated values with nameplate data or instrumentation measurements where available.

Common Power Factor Mistakes

1. Confusing kW and kVA. Real power and apparent power are not the same quantity.
2. Using the wrong voltage. Three-phase calculations normally use line-to-line voltage.
3. Confusing power factor with efficiency. They describe different electrical characteristics.
4. Assuming every motor has the same power factor. Power factor varies with motor and operating conditions.
5. Ignoring system imbalance or harmonics. The simple equations are useful approximations but do not capture every characteristic of a real electrical system.

Quick Reference

Related Calculators

• 3-Phase Motor Current
• Ohm’s Law
• Voltage Divider
• Frequency ↔ RPM