Power · correction
Power Factor
Calculator
Find your power factor and the full power triangle — then size the capacitor to correct it. Raising power factor shrinks the apparent power (kVA) and current you're billed for, without changing the real work (kW). PF = kW ÷ kVA
Built for plant and panel work — clear enough for anyone.
Same 100 kW of real work at three power factors. As PF climbs toward 1.0, the reactive power (kVAR) and apparent power (kVA) collapse toward the real power — that's what correcting the power factor does.
PF · kVA · kVAR
the full power triangle
Correction capacitor kVAR
the exact size to add
Free & private
no signup, runs in your browser
Artie has taught physics and electrical theory for over a decade and consulted on real-world electrical design — so every tool here is grounded in both the theory and the field.
University physics lecturer·Consulted on commercial electrical systems·Last reviewed Jul 2026
Power Factor Calculator
Find power factor — and size the capacitors to correct it.
Enter values to find the power factor.
Enter values to size the correction.
The power triangle
Capacitor kVAR to reach each target — tap to use
Method — the formula for this case
Power factor = real power (kW) ÷ apparent power (kVA); angle φ = arccos(PF); reactive kVAR = √(kVA² − kW²). Correction Qc = kW×(tanφ₁ − tanφ₂). Three-phase uses √3 (1.732) with line-to-line voltage. Capacitance assumes 3φ capacitors in delta; wye per-phase = 3× the delta value.
How to use it
How to use the power factor calculator
Pick a mode: find your power factor from real and apparent power, or correct it to a target. Enter what you know, set the voltage and phase, and read the full power triangle — or the exact capacitor kVAR you need to add.
-
01
Choose a mode
Find power factor from your numbers, or correct it — size the capacitor to hit a target PF.
-
02
Enter what you know
To find: kW plus apparent power (kVA, or V & I). To correct: your load, current PF, and target PF.
-
03
Set voltage, phase & frequency
So it can size the capacitor — the required kVAR, the microfarads, and the before/after current.
-
04
Read the result & size it
Get the full power triangle and PF — or the exact capacitor kVAR to add — then size the wire or breaker.
The core idea
Power factor, and the power triangle
How much of the supplied power actually does work.
Power factor is the ratio of real power (kW) to apparent power (kVA) — how much of what your supply delivers actually does work. PF = cos θ, the angle of the power triangle. At PF 0.8, only 80% of the supplied power is useful.
The power triangle — power factor is the angle
PF runs from 0 to 1 (or 0–100%). At 1.0 all the supplied power does work; below ~0.9 the supply carries extra reactive current for no useful output.
Motors, transformers, welders, coils. Current lags the voltage — the usual cause of a poor power factor, and what you correct by adding capacitors.
Over-correction, or long lightly-loaded cables. Current leads the voltage — utilities penalise this too, and it can push voltage too high.
PF = cos θ = kW ÷ kVA — lagging (inductive) is the common case; correct it with capacitors
The method
The power factor formulas
Two jobs, two families of formula. Find splits real and apparent power into the triangle — power factor is their ratio. Correct sizes the capacitor: the reactive power (kVAR) it must supply to raise the power factor to your target.
PF = kW ÷ kVA = cos θ
kVAR = √(kVA² − kW²)
kVA = kW ÷ PF
Qc = kW × (tan φ₁ − tan φ₂)
C = Qc × 10⁹ ÷ (2π f V²)
Angle & phase — φ = arccos(PF). For three-phase, kVA = √3 × V × I ÷ 1000 (line-to-line).
Capacitance — 1-phase formula shown; three-phase delta = (Qc/3) × 10⁹ ÷ (2π f VLL²) per phase.
PF = kW ÷ kVA · correction removes reactive power, not real power · target 0.95 to clear penalties
Worked example
Correct 100 kW from 0.75 to 0.95
A 100 kW load at 0.75 power factor pulls 133 kVA and 160 amps. Add a 55 kVAR capacitor bank and the power factor climbs to 0.95 — the apparent demand and line current both drop about 21%, with no change to the real work.
angle 1 φ₁ = arccos 0.75 = 41.4° · tan = 0.882
angle 2 φ₂ = arccos 0.95 = 18.2° · tan = 0.329
capacitor Qc = 100 × (0.882 − 0.329) = 55.3 kVAR
One 55 kVAR capacitor bank raises the power factor from 0.75 to 0.95 — dropping apparent demand from 133 to 105 kVA and line current 34 A, with the real work unchanged at 100 kW. Less strain on transformers and cables, and it clears the utility's penalty threshold.
The reference
Power factor by load & why it matters
Most loads sit below 1.0 — motors and welders drag it down, while resistive loads sit at unity. Below about 0.90, utilities often penalise or bill on kVA demand, so 0.95 is the usual correction target.
| Load type | Typical PF |
|---|---|
| Resistive heater · incandescent | 1.0 |
| Induction motor — full load | 0.85 |
| Induction motor — half load | 0.70 |
| Welder · arc furnace | 0.5–0.7 |
| Fluorescent · LED lighting | ~0.9 |
| Fully-loaded transformer | 0.98 |
Typical values — nameplate or measured PF is always better. A motor at part load is the biggest drag.
Aim for 0.95
Clears most penalty thresholds with margin. Chasing a full 1.0 risks over-correction into a leading PF.
Lagging vs leading
Motors and coils lag (the common case); too many capacitors lead. Both are penalised — don't overshoot.
Utility charges
Many utilities bill on kVA demand or add a surcharge below 0.90–0.95. Correction avoids both.
VFDs & non-linear loads
This is displacement PF. Heavy harmonics distort true PF — do a power-quality study before adding capacitors.
Amps, kW, kVA?
For amps ↔ kVA ↔ kW use the Ampere calculator; for watts → amps, Watt-to-Amp →
What affects it
What drags it down — and how you fix it
Power factor drops when reactive loads dominate — lightly-loaded motors, transformers, welders, and VFDs. The fix is capacitors that supply that reactive power locally, sized to a sensible target so you don't over-correct.
What drags it down
the reactive loads
- Lightly-loaded motorsInduction motors at part load are the #1 cause — they draw magnetising current whether or not they're doing work.
- Transformers at light loadA transformer's magnetising current dominates when it's lightly loaded, pulling the power factor down.
- Welders & furnacesWelders, arc furnaces, and induction heating are inherently low-power-factor reactive loads.
- VFDs & non-linear loadsDrives and electronics draw distorted current — a low power factor plus harmonics.
How you fix it
supply the reactive power
- 01Capacitor banksAdd capacitors that supply the reactive power locally, so the supply doesn't have to.
- 02Individual vs centralAt the motor switches with the load; at the switchgear (central) is cheaper to install.
- 03APFC panelsAutomatic PF correction switches capacitor steps in and out as the load varies.
- 04Size to a targetCorrect to about 0.95 — enough to clear penalties without over-correcting.
The point
Correction cuts the kVA and current — not the kW
Capacitors supply the reactive power locally, so the supply carries less. The apparent power (kVA) and line current fall; the real work (kW) — and your kWh — stay exactly the same.
Don't over-correct. Too many capacitors swing you to a leading power factor — also penalised, and it can push voltage too high. With VFDs and non-linear loads, plain capacitors can resonate with harmonics — do a power-quality study before sizing a bank.
Quick chart
The correction-factor table
The industry shortcut: find your current power factor and your target, read the multiplier, and multiply by your load in kW to get the capacitor kVAR. From 0.75 to 0.95 the multiplier is 0.553 — so 100 kW needs 55.3 kVAR.
Multiplier k = tan(arccos PF₁) − tan(arccos PF₂). Capacitor kVAR = k × kW.
Capacitor needed
55.3 kVAR
0.553 × 100 kW
Multiplier k — current PF → target PF
| Current PF | → 0.90 | → 0.95 | → 1.00 |
|---|---|---|---|
| 0.70 | 0.536 | 0.692 | 1.020 |
| 0.72 | 0.480 | 0.635 | 0.964 |
| 0.75 | 0.398 | 0.553 | 0.882 |
| 0.78 | 0.318 | 0.474 | 0.802 |
| 0.80 | 0.266 | 0.421 | 0.750 |
| 0.82 | 0.214 | 0.369 | 0.698 |
| 0.85 | 0.135 | 0.291 | 0.620 |
| 0.88 | 0.055 | 0.211 | 0.540 |
| 0.90 | 0.000 | 0.156 | 0.484 |
Read your current PF row, your target column, then multiply by your kW load. Capacitor kVAR = k × kW.
| Current PF | →0.85 | →0.90 | →0.92 | →0.95 | →0.98 | →1.00 |
|---|---|---|---|---|---|---|
| 0.60 | 0.714 | 0.849 | 0.907 | 1.005 | 1.130 | 1.333 |
| 0.65 | 0.549 | 0.685 | 0.743 | 0.840 | 0.966 | 1.169 |
| 0.70 | 0.400 | 0.536 | 0.594 | 0.692 | 0.817 | 1.020 |
| 0.75 | 0.262 | 0.398 | 0.456 | 0.553 | 0.679 | 0.882 |
| 0.80 | 0.130 | 0.266 | 0.324 | 0.421 | 0.547 | 0.750 |
| 0.85 | 0.000 | 0.135 | 0.194 | 0.291 | 0.417 | 0.620 |
| 0.90 | 0.000 | 0.000 | 0.058 | 0.156 | 0.281 | 0.484 |
What is power factor?
Power factor is the ratio of real power (kW) to apparent power (kVA) — how much of the power your supply delivers actually does useful work. It runs from 0 to 1; at 0.8, only 80% of the supplied power is doing work.
How do I calculate power factor?
Divide real power by apparent power: PF = kW ÷ kVA. It's also the cosine of the phase angle. From measurements, find kVA first (kVA = V × I ÷ 1000, × √3 for three-phase), then divide the kW into it.
What is a good power factor?
Above 0.95 is excellent, and most utilities want at least 0.90 to 0.95. Below about 0.85 is poor — you're drawing extra reactive current for no useful output, and you may face penalties.
How do I improve power factor?
Add capacitors that supply the reactive power right at the load, so the supply carries only the real kW. For a whole plant, an automatic capacitor bank (APFC) steps in and out as the load varies.
What size capacitor do I need?
The required capacitor kVAR = kW × (tan φ₁ − tan φ₂), where φ is arccos of each power factor. Or read the correction-factor table: multiply your kW by the factor for your current and target PF.
What's the difference between leading and lagging power factor?
Lagging means the current lags the voltage — the usual case with inductive loads like motors. Leading means it leads, from capacitive loads or over-correction. Utilities penalise both.
Does correcting power factor save money?
It lowers your apparent (kVA) demand and line current, and clears utility power-factor penalties — but it doesn't reduce the real energy (kWh) you use. Whether it pays back depends on your tariff.
Why do utilities penalise low power factor?
A low power factor means the grid must carry extra current for the same real work — sizing transformers and cables for capacity that does nothing useful. Many utilities bill on kVA demand or add a surcharge to recover that cost.
Keep going
Related electrical calculators
Power factor sits between the current and the power. These pick up on either side: convert amps to kVA and kW, turn watts into amps, and size the conductor.
How we keep this accurate
Calculations use the standard relationships — PF = kW ÷ kVA, Qc = kW × (tan φ₁ − tan φ₂), × √3 for three-phase — and give displacement power factor. Results are for planning and screening. Capacitor ratings, harmonics, switching, and utility tariffs vary — confirm with equipment data and a licensed engineer before installing correction.