Calculate AC Power
Enter RMS voltage, RMS current, and power factor.
What Is an AC Power Calculator?
An AC power calculator helps determine the different forms of power in an alternating-current circuit. Unlike a simple DC power calculation, AC circuits may have a phase difference between voltage and current.
This calculator uses RMS voltage, RMS current, and power factor to calculate real power in watts, apparent power in volt-amperes, reactive power in VAR, and the associated phase angle.
AC Power Formulas
For a single-phase AC circuit, apparent power is the product of RMS voltage and RMS current. Real power is the portion that performs useful work, while reactive power represents energy exchanged with reactive components.
P = V × I × PF
φ = cos-1(PF)
Q = V × I × sin(φ)
S² = P² + Q²
Here, P is real power in watts, S is apparent power in VA, Q is reactive power in VAR, PF is power factor, and φ is the phase angle.
How to Use the AC Power Calculator
- Enter the RMS voltage and choose mV, V, or kV.
- Enter the RMS current and choose mA, A, or kA.
- Enter a power factor between 0 and 1.
- Select whether the power factor is leading or lagging.
- Optionally enter your AC frequency.
- Click Calculate AC Power.
The tool instantly displays real power, apparent power, reactive power, phase angle, and the entered power factor.
AC Power Calculation Example
Suppose a single-phase load operates at 230 V and draws 10 A with a lagging power factor of 0.80.
S = 2300 VA
P = 230 × 10 × 0.80
P = 1840 W
φ = cos-1(0.80)
φ ≈ 36.87°
Q ≈ 1380 VAR
This means the load consumes about 1.84 kW of real power while the apparent power supplied by the source is 2.30 kVA.
Real, Apparent and Reactive Power Explained
Real Power
Real power is the portion of electrical power that performs useful work such as producing heat, light, or mechanical motion. It is measured in watts.
Apparent Power
Apparent power is the product of RMS voltage and RMS current. It is measured in volt-amperes and represents the total power demand on the source.
Reactive Power
Reactive power represents energy that alternately moves between the source and reactive components such as inductors and capacitors. It is measured in VAR.
What Is Power Factor?
Power factor is the ratio of real power to apparent power. A value of 1 represents an ideal purely resistive load where voltage and current are in phase.
Lower power factor means more current may be required to deliver the same amount of useful real power. Motors, transformers, and other inductive loads commonly operate with a lagging power factor.
Leading vs Lagging Power Factor
Lagging Power Factor
A lagging power factor is commonly associated with inductive loads. Current lags voltage and reactive power is conventionally considered positive.
Leading Power Factor
A leading power factor is commonly associated with capacitive behavior. Current leads voltage and reactive power can be represented as negative.
Unity Power Factor
At a power factor of 1, the phase angle is zero and real power equals apparent power for an ideal load.
Common AC Power Units
| Quantity | Symbol | Common Unit |
|---|---|---|
| Voltage | V | Volts |
| Current | I | Amperes |
| Real Power | P | Watts (W) |
| Apparent Power | S | Volt-amperes (VA) |
| Reactive Power | Q | Volt-ampere reactive (VAR) |
| Power Factor | PF | Unitless |
| Phase Angle | φ | Degrees (°) |
Frequently Asked Questions
How do you calculate AC power?
For a single-phase AC circuit, real power can be calculated using P = V × I × PF, where V and I are RMS values and PF is the power factor.
What is the difference between watts and VA?
Watts measure real power that performs useful work, while VA measures apparent power, which is the product of RMS voltage and RMS current.
What is reactive power?
Reactive power is energy exchanged between the source and reactive components such as inductors and capacitors. It is measured in VAR.
What is a good power factor?
A power factor closer to 1 indicates that a larger portion of the apparent power is being converted into useful real power.
What is unity power factor?
Unity power factor means PF = 1. In an ideal circuit, voltage and current are in phase and reactive power is zero.
Can this calculator calculate phase angle?
Yes. It calculates the phase angle using φ = cos⁻¹(PF) and adjusts the sign according to whether the selected power factor is leading or lagging.