Power Factor Calculator
Find power factor and reactive power from real and apparent power.
Power Factor Calculator
Power factor measures how efficiently an AC load converts apparent power (volt-amps) into real power (watts). A power factor of 1.0 means all current does useful work; lower values mean extra current circulates without delivering proportional real power.
This calculator takes real power in kilowatts (kW) and apparent power in kilovolt-amperes (kVA) and returns power factor and reactive power in kVAR. Utilities, generators, and transformers are often rated in kVA—knowing PF links that rating to real kilowatts your equipment can deliver.
Use it to understand motor loads, size generators, or interpret meter data. Pair with the watts-to-amps and amps-to-watts calculators when you need line current at a known voltage and power factor.
How this calculator works
- Enter real power (kW)—the actual work done: heating, mechanical output, or useful electrical load.
- Enter apparent power (kVA)—volts × amps ÷ 1000 for the circuit, or nameplate kVA.
- Apparent power must be ≥ real power; otherwise power factor would exceed 1, which is not physical for passive loads.
- Power factor = kW ÷ kVA (capped at 1.0 in results).
- Reactive power kVAR = √(kVA² − kW²)—the magnetizing or stored-energy component.
Core power factor relationships
PF = kW ÷ kVA | kVAR = √(kVA² − kW²) | kVA² = kW² + kVAR²
Real power (kW) does work. Reactive power (kVAR) oscillates between source and load without net consumption—typical of motors and transformers. Apparent power (kVA) is the vector combination: kVA² = kW² + kVAR². Power factor is the cosine of the phase angle between voltage and current; PF = kW/kVA when both are in consistent units.
Formulas used by this tool
- Power factor = real power (kW) ÷ apparent power (kVA).
- Reactive power (kVAR) = √(kVA² − kW²).
- Apparent power must be greater than or equal to real power.
Worked example: 2.4 kW, 3 kVA
A workshop machine draws 2.4 kW real power with 3 kVA apparent on the meter.
- Power factor = 2.4 ÷ 3 = 0.8.
- kVAR = √(3² − 2.4²) = √(9 − 5.76) = √3.24 ≈ 1.8 kVAR reactive.
- At 120 V single-phase, apparent amps ≈ 3,000 VA ÷ 120 ≈ 25 A; real watts still 2,400 W.
- Improving PF toward 1.0 reduces current for the same kW—useful for generator and wire sizing.
Practical tips
- Resistive loads (heaters, incandescent) run near PF 1.0; induction motors often 0.7–0.9.
- kVA on a generator nameplate is apparent—multiply by expected PF for real kW capacity.
- Low PF increases current, causing larger wire, breaker, and transformer needs for the same kW.
- Power factor correction capacitors reduce kVAR on motor circuits in industrial settings.
- Do not enter kW greater than kVA—the tool assumes valid input; PF cannot exceed 1 for passive loads.
Frequently asked questions
What is a good power factor?
Unity (1.0) is ideal—all apparent power is real power. Many utilities charge industrial customers for low PF below 0.9–0.95. Residential loads are often mixed; motors and HVAC may run 0.8–0.95. Higher is better for efficiency and current draw.
What is the difference between kW, kVA, and kVAR?
kW is real power (work). kVA is apparent power (volts × amps scaled). kVAR is reactive power (non-working component). They relate as a right triangle: kVA is the hypotenuse, kW and kVAR are the legs.
Why does low power factor matter?
For the same real kW, lower PF requires higher apparent kVA and higher amps. Cables, breakers, and generators must be sized for amps (kVA), not just watts. Low PF also wastes distribution capacity on reactive circulation.
Does this apply to DC circuits?
No. DC has no phase angle between voltage and current; power factor is effectively 1. Use watts-to-amps or Ohm's law for DC. This calculator is for AC real vs apparent power.
How do I get kVA from volts and amps?
Single-phase: kVA = (volts × amps) ÷ 1000. Three-phase line values use different formulas with √3. Enter the kVA figure from your meter, nameplate, or calculation into this tool with known kW.
How does this relate to the watts-to-amps calculator?
Watts-to-amps uses PF as an input with watts and volts to find amps. This calculator derives PF from kW and kVA and also finds kVAR. Use this when you have metered kW and kVA; use watts-to-amps when you already know PF and need current.
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