The Current That Does No Work
Feed AC into a coil and the current is lazy: it peaks after the voltage peaks, because the coil stores energy in its magnetic field and gives it back a quarter-cycle later. The grid has to carry that sloshing current — it heats wires, transformers, and generator windings — but the site never converts it to work. That is the reactive current, and it is why a factory floor meter can read 2,250 VA while the machines inside only do 1,800 W of useful power. The ratio of the two numbers is the power factor: 0.8 in this case, and every 0.1 of PF lost is real money on a commercial tariff.
PF = watts ÷ volt-amps = cos φ
PF = P / S
PF runs 0 to 1 — 1.0 is pure resistance; the phase angle φ = arccos(PF).
Where the PF Numbers Come From
| Load | Typical PF | Why |
|---|---|---|
| Heater, incandescent lamp | 1.0 | Pure resistance — voltage and current in phase. |
| LED driver, PFC supply | 0.9–0.99 | Active correction circuits pull current in phase on purpose. |
| Induction motor, loaded | 0.75–0.85 | Windings store magnetic energy — the classic lagging load. |
| Induction motor, idling | 0.2–0.4 | Almost no real work but full magnetizing current. |
| Old fluorescent ballast | 0.5–0.7 | Choke coil with no correction — the reason ballasts were regulated. |
The idling-motor row is the one that surprises plant managers: a motor spinning a conveyor belt with nothing on it still draws its full magnetizing current, so its PF collapses toward 0.3. A factory full of lightly loaded motors can sit below 0.6 — and the standard fix is a capacitor bank sized to supply the reactive current locally. The capacitor's current leads the voltage, canceling the motor's lag, and the site's PF climbs back above 0.9. That is why the kVA to kW and kW to kVA pages matter here: PF is the coefficient in both.
Engineering Context
Power factor is the bridge between the two other AC power converters in this family: kVA to kW applies it as a multiplier, and kW to kVA as a divisor. For single-phase loads the volt-amps are simply volts × amps at the branch circuit — see volts to amps and amps to volts. Motors, the biggest PF offenders, are rated in horsepower, and the energy those corrected loads consume is billed in kilowatt-hours. The whole set returns to the electric hub.
More: kVA to kW · kW to kVA · V to A · Electric Hub
Related Unit Converters
Frequently Asked Questions
How do I calculate power factor?
Divide real power by apparent power: PF = watts ÷ volt-amps. A motor drawing 1,800 W while the meter shows 2,250 VA runs at 1,800 ÷ 2,250 = 0.8. The result is always between 0 and 1, and it is the cosine of the phase angle between voltage and current.
Why do utilities charge extra for low power factor?
Because low-PF current still heats the utility's wires, transformers, and generators without doing useful work. A site at 0.7 PF needs roughly 43% more current to deliver the same kW as a site at 1.0 — so the utility's distribution losses are higher and less of its capacity is usable. Many commercial tariffs apply a penalty below 0.9 or 0.95, which is why capacitor banks are installed: correcting PF from 0.7 to 0.95 cuts the current draw by over a quarter.
Can power factor be higher than 1?
No. Real power can never exceed apparent power, so PF is mathematically capped at 1.0, which is where pure resistive loads (heaters, incandescent lamps) sit. A leading PF (below 1 but capacitive rather than inductive) can occur on cable-heavy or over-corrected systems, and some utilities penalize leading PF too, because it pushes voltage up.