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Power Factor Calculator

Calculate real, reactive, and apparent power relationships, power factor correction, and power triangle analysis for AC circuits. Get step-by-step breakdown with formulas.

Power Factor Calculator
Quick Examples
Enter Voltage, Current & Real Power
V Voltage
I Current
P Real Power
Enter Real Power & One Known Value
P Real Power
? Known Value
Power Factor Correction Parameters
P Real Power
Current PF (lagging)
Target PF
V System Voltage
Frequency

Embed Power Factor Calculator Widget

About Power Factor Calculator

The Power Factor Calculator analyzes the relationship between real power (P), reactive power (Q), and apparent power (S) in AC electrical circuits. Enter your known values to compute the power factor, phase angle, power triangle, and — for correction scenarios — the required capacitor to improve a lagging power factor.

What Is Power Factor?

Power factor (PF) is the ratio of real (useful) power to apparent power in an AC circuit. It indicates how effectively electrical power is being used. A power factor of 1.0 (unity) means all the power delivered is being used productively, while a lower power factor means more current is needed to deliver the same real power.

$$PF = \cos(\theta) = \frac{P}{S}$$

where \(P\) is real power in watts (W), \(S\) is apparent power in volt-amperes (VA), and \(\theta\) is the phase angle between voltage and current.

The Power Triangle

The power triangle is a right triangle that visualizes the relationship between the three types of power in an AC circuit:

$$S^2 = P^2 + Q^2$$

Power Factor Correction

Most industrial loads (motors, transformers, fluorescent lighting) are inductive and draw a lagging current, resulting in a low power factor. Correction capacitors are connected in parallel to supply the reactive power locally, reducing the reactive power drawn from the supply:

$$Q_C = P \times \left(\tan(\theta_1) - \tan(\theta_2)\right)$$
$$C = \frac{Q_C}{2\pi f V^2}$$

where \(Q_C\) is the capacitor reactive power, \(\theta_1\) and \(\theta_2\) are the original and target phase angles, \(f\) is the system frequency, and \(V\) is the system voltage.

How to Use This Calculator

  1. Select a calculation mode — Choose "From Voltage & Current" if you know V, I, and P; "From Power Values" if you know P and one of S, Q, or PF; or "Power Factor Correction" to size a correction capacitor.
  2. Enter your values — Fill in the required fields with appropriate units.
  3. Calculate — Click the "Calculate Power Factor" button.
  4. Review results — Examine the power factor, phase angle, power triangle diagram, and step-by-step formulas.

Practical Applications

FAQ

What is power factor?

Power factor is the ratio of real power (P) to apparent power (S) in an AC circuit, expressed as PF = P/S = cos(θ). It ranges from 0 to 1, where 1 means all power is used effectively. Most industrial loads have a lagging power factor due to inductive equipment like motors and transformers.

What is the power triangle?

The power triangle is a right triangle representing the relationship between real power (P in watts), reactive power (Q in VARs), and apparent power (S in VA). Real power forms the horizontal side, reactive power the vertical side, and apparent power the hypotenuse. The angle between P and S is the phase angle θ, and cos(θ) equals the power factor.

Why is power factor correction important?

Low power factor means higher current is drawn for the same real power, leading to increased line losses, voltage drops, and higher utility bills. Many utilities charge penalties for power factors below 0.85–0.90. Correction capacitors reduce reactive power demand, lower current draw, free up transformer capacity, and improve voltage regulation.

How do you calculate the correction capacitor?

The correction capacitor is sized using C = QC / (2πfV²), where QC is the reactive power to be compensated, f is the system frequency, and V is the system voltage. QC equals P × (tan(θold) − tan(θnew)), where θ values come from the current and target power factors.

What is the difference between leading and lagging power factor?

A lagging power factor occurs when current lags behind voltage, typical of inductive loads like motors and transformers. A leading power factor occurs when current leads voltage, typical of capacitive loads. Most industrial and residential loads have a lagging power factor, which is why correction capacitors are added to compensate.

Reference this content, page, or tool as:

"Power Factor Calculator" at https://MiniWebtool.com/power-factor-calculator/ from MiniWebtool, https://MiniWebtool.com/

by miniwebtool team. Updated: Mar 18, 2026

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