Power Factor Correction Calculator
Calculates the reactive power (kVAR) of capacitors needed to raise a facility's power factor to a target value. Use it to reduce utility demand charges and improve electrical system efficiency.
About this calculator
Power factor (PF) is the ratio of real power (kW) to apparent power (kVA) in an AC circuit. A low power factor means the system draws more current than necessary, increasing losses and utility penalties. Correction is achieved by adding capacitor banks that supply reactive power locally, reducing the reactive demand seen by the utility. The required capacitor size in kVAR is given by: Q_C = P × (tan(arccos(PF_current)) − tan(arccos(PF_target))), where P is real power in kW, PF_current is the existing power factor, and PF_target is the desired power factor. The arccos converts power factor to the phase angle θ, and tan(θ) gives the ratio of reactive to real power. Subtracting the target reactive ratio from the current one yields the reactive power that capacitors must supply. Most utilities require a power factor of at least 0.90–0.95 to avoid surcharges.
How to use
Assume a facility draws 100 kW of real power at a current power factor of 0.75 and wants to reach a target power factor of 0.95. Step 1: arccos(0.75) ≈ 41.41°, tan(41.41°) ≈ 0.8819. Step 2: arccos(0.95) ≈ 18.19°, tan(18.19°) ≈ 0.3287. Step 3: Q_C = 100 × (0.8819 − 0.3287) = 100 × 0.5532 ≈ 55.32 kVAR. You would need to install approximately 55.32 kVAR of capacitor banks. Enter realPower = 100, currentPF = 0.75, and targetPF = 0.95 to verify the result instantly.
Frequently asked questions
Why does a low power factor increase my electricity bill?
Utilities measure both real power (kW) and apparent power (kVA). When power factor is low, the current flowing through cables and transformers is higher than required to do useful work, causing resistive losses and reducing system capacity. Many commercial and industrial tariffs include a demand charge or a power factor penalty that is triggered when PF falls below a threshold such as 0.90. Installing capacitors to raise the power factor reduces apparent power demand, directly lowering these charges and freeing up transformer capacity for additional loads.
How do I choose the right capacitor kVAR rating for power factor correction?
Use this calculator to find the theoretical kVAR needed, then select a standard capacitor bank size that meets or slightly exceeds that value. Capacitors are available in fixed steps (e.g., 25, 50, 100 kVAR) or as automatic banks with multiple switchable stages. For facilities with highly variable loads, an automatic power factor correction (APFC) panel that switches capacitor stages in and out is preferable to a single fixed bank, ensuring the power factor stays near the target across the full load range.
What happens if I over-correct power factor by adding too much capacitance?
Over-correction occurs when the installed capacitor kVAR exceeds what is needed, pushing the power factor leading rather than lagging. A leading power factor can cause voltage rise, instability in lightly loaded systems, and may trigger different utility penalties. It can also interfere with the operation of voltage regulators and automatic tap changers on transformers. To avoid over-correction, size capacitors conservatively, use an automatic bank for variable loads, and confirm the final power factor with a power quality analyzer after installation.