Power Factor Correction Calculator
Calculate the capacitor kvar needed to correct a power factor to a target value, and size the bank itself — capacitance in µF per phase for a delta or star connection, capacitor current, and the apparent power and line current before and after correction.
Input
The active load being corrected — the kW your meter reads.
Lagging power factor of the uncorrected load, between 0.05 and 1.
Where you want to end up. Utilities commonly require 0.95 or better.
Line-to-line voltage on a three-phase supply, line-to-neutral on single-phase.
Delta needs a third of the capacitance but rates the units for full line voltage.
Output
| Quantity | Before | After |
|---|---|---|
| No data yet | ||
| Item | Value |
|---|---|
| No data yet | |
Guides
Inductive loads — motors, transformers, welders, fluorescent ballasts — draw reactive current that does no useful work but still fills your cables and shows up on the bill. Correction capacitors supply that reactive power locally instead. This calculator works out how many kvar it takes to reach your target power factor, and then sizes the capacitor bank itself in microfarads.
How to use it
- Enter the real power of the load in kW — the active figure your meter reads.
- Enter the existing power factor and the target power factor. Utilities commonly penalise anything below 0.95.
- Pick three-phase or single-phase, then the supply voltage (line-to-line for three-phase) and the frequency.
- On a three-phase supply, choose whether the bank is wired delta or star.
You get two tables: a before/after comparison of power factor, reactive power, apparent power and line current, and a capacitor-bank specification with the required kvar, the capacitance per phase, the capacitor current and the kVA freed up on your transformer.
The formulas
φ = acos(pf)— the phase angleQ = P × tan φ— reactive power in kvarQc = P × (tan φ₁ − tan φ₂)— the compensation needed, the classic "kvar per kW" table multiplierS = P ÷ pf— apparent power in kVAI = S ÷ (√3 × V)three-phase, orS ÷ Vsingle-phase
The capacitance follows from Qc = V² × 2πf × C:
- single-phase:
C = Qc ÷ (2πf V²) - three-phase delta:
C = (Qc ÷ 3) ÷ (2πf V²)— each unit sees the full line voltage - three-phase star:
C = (Qc ÷ 3) ÷ (2πf (V/√3)²), which is three times the delta value
Delta or star?
Delta needs only a third of the capacitance for the same kvar, which is why most low-voltage banks are wired that way — but each capacitor has to be rated for the full line voltage. Star capacitors only see phase voltage, so they can be cheaper units, at the cost of three times the µF. The calculator shows both the capacitor voltage and the resulting capacitance so the trade-off is explicit.
Why does the line current drop?
Because the current a cable carries is set by apparent power, not real power. Correcting 100 kW from 0.75 to 0.95 cuts apparent power from 133 kVA to 105 kVA — the same useful work, about 21% less current, and that headroom is released back to the transformer and the feeders.
Can I over-correct?
Don't aim for unity. A bank sized for full load becomes leading at part load, which raises voltage, can cause resonance with system inductance, and some tariffs penalise leading power factor too. 0.95–0.98 with automatic switching steps is the normal target.
Is this enough to order a bank?
It's the sizing starting point, not the design. Harmonic distortion (which may require detuned reactors), switching-step granularity, inrush current, capacitor duty ratings, voltage level and utility rules all need an engineering review before you buy.
Privacy
Everything is calculated in your browser. No values are sent to a server.
Related tools
To check the current-carrying capacity of the feeders the correction frees up, use the Wire Size Calculator. For the underlying voltage, current and resistance relationships, the Ohm's Law Calculator covers them, and the Electricity Cost Calculator turns the kW figure into a running cost.