Power Factor Correction Calculator
Power factor correction uses capacitor banks to compensate for the reactive power drawn by inductive loads (motors, transformers, fluorescent lighting). The required capacitor size in kVAR is calculated using the IEEE formula: kVAR = kW x (tan(arccos(PF_old)) - tan(arccos(PF_new))). Enter your facility's real power demand, current power factor, and target power factor to compute the required capacitor bank size and the resulting reduction in apparent power (kVA).
Power factor correction formula (IEEE Standard 141)
kVA(old) = kW / PF(old)
kVAR(old) = sqrt(kVA(old)^2 - kW^2)
Required kVAR = kW x (tan(arccos(PF_old)) - tan(arccos(PF_new)))
kVA(new) = kW / PF(new)
kVA Reduction = kVA(old) - kVA(new)
This formula is from IEEE Standard 141-1993 (IEEE Red Book: Recommended Practice for Electric Power Distribution for Industrial Plants), Chapter 8, Section 8.3. The tan(arccos(PF)) term converts power factor to the tangent of the phase angle, which directly represents the ratio of reactive to real power.
Power factor correction benefits
- Reduces utility demand charges (many utilities charge per kVA, not just kW).
- Reduces I^2R losses in cables, transformers, and switchgear, saving energy and reducing heat.
- Improves voltage regulation and reduces voltage drop under load.
- May allow smaller-rated transformers and switchgear when planning new facilities.
- IEEE Standard 141 recommends installing capacitors as close to the inductive load as possible (load-side correction) for maximum loss reduction.
Power factor correction: frequently asked questions
What is power factor and why does it matter?
Power factor (PF) is the ratio of real power (kW, which does useful work) to apparent power (kVA, which is drawn from the supply). PF = cos(theta), where theta is the phase angle between voltage and current. A PF of 1.0 is ideal. Low power factor (caused by inductive loads like motors and transformers) increases current draw, causes voltage drops, and results in utility demand charges.
What is the formula for power factor correction capacitor sizing?
Required kVAR = kW x (tan(arccos(PF_old)) - tan(arccos(PF_new))). This is the standard IEEE formula for capacitor bank sizing. kW is real (active) power. PF_old is current power factor. PF_new is target power factor. The result is the reactive power (kVAR) that must be supplied by the capacitor bank.
What is a typical target power factor for industrial facilities?
Most utilities impose demand charges or penalties when power factor falls below 0.85-0.90. IEEE Standard 141 (Red Book) recommends maintaining PF at 0.90-0.95 for industrial systems. Some utilities require PF greater than 0.95. Correcting to 1.0 is generally not economical due to the cost of precise capacitor sizing.
What is the difference between real power, reactive power, and apparent power?
Real power (kW) does actual work (heats, lights, drives loads). Reactive power (kVAR) is exchanged between inductive/capacitive loads and the supply without doing useful work. Apparent power (kVA) = square root(kW squared + kVAR squared). Power factor = kW/kVA. Capacitors supply reactive power locally, reducing the reactive current that must come from the utility.
How does power factor correction save money?
Utilities bill large commercial and industrial customers based on both kW demand and kVA (or kVAR). By adding capacitors, you reduce kVAR demand from the grid, which reduces kVA and often avoids demand surcharges. Additionally, lower current in cables and transformers reduces resistive losses (I^2 x R losses), saving energy and extending equipment life.
Official sources
- IEEE Standard 141-1993 (IEEE Red Book): Recommended Practice for Electric Power Distribution for Industrial Plants. IEEE, 1993.
- DOE Office of Industrial Technologies: Improving Power Factor to Reduce Energy Costs (DOE).
- NEMA: NEMA MG-1: Motors and Generators.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.