{{ summaryTitle }}{{ summaryValue }}{{ summaryLine }}{{ badge.label }}{{ badge.value }}

Enter the active load in kilowatts.
kW
Enter the measured or rated apparent power in kilovolt-amperes.
kVA
Most motors and transformers are lagging; use leading only when metering confirms capacitive behavior.
Typical planning targets are 0.90 to 0.97. Confirm the actual utility or equipment requirement before installation.
PF
Zero is neutral and omits capacitance sizing. For three-phase connections, enter line-to-line voltage.
V RMS
Used only when voltage is nonzero and capacitive correction is required.
Use the actual supply frequency; 60 Hz is the presentation default.
Hz
Three decimal places is the neutral presentation default.
MeasureValueMeaningCopy
{{ row.measure }}{{ row.value }}{{ row.note }}
DecisionResultNext stepCopy
{{ row.decision }}{{ row.result }}{{ row.action }}
Impedance Calculator Calculate ideal series RLC impedance from reactances or component values with phase, power factor, current and resonance results.
Voltage Divider Calculator Size or analyze a loaded voltage divider and check preferred resistor values, output sag plus tolerance, current and power before building.
Wire Gauge Calculator Size an AWG conductor with voltage-drop and ampacity checks using current, run length, material and a temperature reference column.
Resistor Combination Finder Find practical resistor networks for a target value, rank nominal error, and screen stock tolerance and per-part power stress before building.

An alternating-current source must carry the full electrical load even when part of that load is only exchanging energy with magnetic or electric fields. Motors, transformers, welding equipment, discharge lighting, and lightly loaded power supplies can therefore occupy conductor, transformer, or generator capacity without turning all of that capacity into useful work.

Power factor describes that utilization at one operating point. It is the ratio of real power in kilowatts (kW) to apparent power in kilovolt-amperes (kVA). A value of 0.80 means that 80% of the apparent-power magnitude appears as real power. Moving the ratio closer to 1 can reduce current and apparent demand for the same kW load, but it does not reduce the useful power the equipment needs.

Real power
The kW converted into mechanical work, heat, light, or another net energy output.
Apparent power
The kVA magnitude the source and conductors must supply.
Reactive power
The kVAR associated with energy that moves into and out of fields during each AC cycle.
Phase angle
The displacement between sinusoidal voltage and current; its cosine is displacement power factor.
Power triangle comparing current apparent power with a higher power-factor target at the same real power
Same kW, less reactive power, lower kVA. P = real power; Q = reactive power; S = apparent power. The dashed line is the higher power-factor target.

The direction of reactive power changes the correction. An inductive load normally has lagging current and positive reactive power, so a capacitor bank can supply an opposing capacitive contribution. A leading load is already capacitive; adding more capacitance can worsen overcorrection, so its remedy may require inductive compensation or a change in switching strategy.

Power factor is often checked while sizing generators and transformers, investigating utility demand charges, or reviewing a motor-heavy plant. The measurement must represent the operating case that matters. A reading taken with one production line idle cannot safely stand in for peak operation, and a correction bank sized for full load may push a lightly loaded system into leading power factor.

The familiar power triangle is a sinusoidal steady-state model. Harmonic current, distorted voltage, rapid load cycling, resonance, switching transients, equipment tolerances, and utility tariff rules need a fuller power-quality study. Treat calculated kVAR and microfarads as planning values, not as an installation specification.

How to Use This Tool:

Start with real and apparent power measured for the same load and time interval. The correction estimate is only as representative as that pair of readings.

  1. Enter Real power in kW and Apparent power in kVA. Apparent power must be at least as large as real power.
  2. Choose Reactive direction. Use lagging for a confirmed inductive load and leading only when metering confirms capacitive behavior.
  3. Set the Target power factor required by the utility, generator study, or equipment plan. A target at or below the current power factor produces no correction request.
  4. Review the current power factor, signed kVAR, corrected kVA, and apparent-demand reduction before considering hardware.
  5. Enter nonzero RMS voltage, the capacitor connection, and supply frequency only when a capacitive correction needs a per-phase microfarad estimate. For a three-phase connection, use line-to-line voltage.

Interpreting Results:

The current power factor and signed reactive power describe the entered operating point. Positive kVAR means lagging, inductive behavior; negative kVAR means leading, capacitive behavior. The correction magnitude is the reactive-power change needed to reach the applied target while holding real power constant.

  • No correction required means the requested target does not exceed the current power factor. It does not certify the installation under every load condition.
  • Capacitive correction is the expected result for a lagging load. Verify the bank in steps across the actual load range.
  • Inductive correction identifies a leading load. A capacitor microfarad value is deliberately not produced for this case.
  • Corrected apparent power is a modeled kVA value at the same kW. Compare it with conductor, transformer, generator, and tariff limits rather than reading it as energy savings.

Technical Details:

For a sinusoidal load, real power, reactive power, and apparent power form a right triangle. Real power is the horizontal component, signed reactive power is the vertical component, and apparent power is the hypotenuse. Reducing the reactive component while holding kW fixed shortens the hypotenuse and raises power factor.

Formula Core

Power factor is real power divided by apparent power.

PF=PS

The reactive-power magnitude follows from the other two sides of the power triangle. Direction is applied after the magnitude is found.

|Q|=S2−P2

The target reactive magnitude is based on the target phase angle. The required compensation is the signed target kVAR minus the signed current kVAR.

Qt=P⁢tan(arccos(PFt))
Qc=Qt−Q
SymbolMeaningUnit
PReal powerkW
SApparent power before correctionkVA
QSigned current reactive powerkVAR
PFtApplied target power factorRatio
QcSigned compensation; negative is capacitive and positive is inductivekVAR

Corrected apparent power is P divided by the applied target power factor. Apparent-demand reduction is the current kVA minus corrected kVA, and the displayed percentage divides that reduction by current kVA. If the target is no higher than the current ratio, the current power factor becomes the applied target and all correction values remain zero.

Per-phase capacitance

A microfarad estimate is available only for capacitive correction with voltage above zero. The calculation converts total correction kVAR to VAR and divides by angular frequency and voltage squared.

Cphase=|Qc|×1000d×2πfV2×106

Here f is frequency in hertz, V is RMS voltage in volts, and d is 3 for a three-phase delta connection or 1 for single-phase and three-phase wye. Real and apparent power must both be positive, with kVA at least equal to kW. The accepted target is 0.5 through 1.0, voltage is 0 through 1,000,000 V RMS, and frequency is 1 through 1,000 Hz. All calculations retain full precision; the Display precision choice changes presentation only.

Accuracy and Installation Safety:

The equations assume steady sinusoidal quantities and a representative operating point. Before equipment selection, verify:

  • real power, apparent power, and reactive direction with suitable metering across minimum, typical, and peak load;
  • utility power-factor rules and whether billing uses displacement power factor, true power factor, kVA demand, or another measure;
  • harmonic spectrum and resonance risk, especially with drives, rectifiers, UPS systems, and other nonlinear loads;
  • bank step size, contactor or thyristor switching, inrush, discharge, enclosure, protection, voltage tolerance, and temperature rating; and
  • the applicable electrical code and a qualified engineer's or electrician's site study before energizing correction equipment.

Worked Examples:

Lagging load corrected toward 0.95

An 8 kW load measured at 10 kVA has a power factor of 0.80 and 6 kVAR of lagging reactive power. A 0.95 target has about 2.629 kVAR of lagging reactive power at the same kW, so the required change is about 3.371 kVAR capacitive. Corrected apparent power is about 8.421 kVA, a modeled reduction of about 1.579 kVA or 15.8%. Voltage left at zero correctly withholds the microfarad estimate.

References: