The AC Wattage Calculator computes real power (watts), apparent power (VA), reactive power (VAR), and power factor for alternating current circuits. Enter voltage, current, and phase angle to analyze single-phase AC power — essential for electrical engineering, HVAC sizing, and generator selection.
1,020
W
1,200
VA
632.14
VAR
—
°
1.02
kW
1.2
kVA
1,020
W
1,200
VA
632.14
VAR
—
°
1.02
kW
1.2
kVA
The calculator for AC wattage determines the three components of AC power — real power (W), apparent power (VA), and reactive power (VAR) — along with the power factor that relates them. Unlike DC circuits where power equals voltage times current, AC circuits involve a phase difference between voltage and current that splits power into useful (real) and non-useful (reactive) components.
The three AC power quantities form a right triangle known as the power triangle:
The relationship between them is: S² = P² + Q². A purely resistive load (heater, incandescent bulb) has φ = 0, making real power equal to apparent power. Inductive loads (motors, transformers) introduce a lagging phase angle that increases reactive power and reduces efficiency. The RMS voltage calculator provides the correct voltage input for AC power calculations.
Power factor (PF = cos φ) measures how efficiently electrical power is being used. A power factor of 1.0 means all supplied power performs useful work; a power factor of 0.7 means only 70% of the apparent power is doing useful work. Low power factor matters because:
Power factor correction is achieved by adding capacitor banks to offset inductive reactive power. Use this online calculator to determine how much reactive power must be compensated. The inductive reactance calculator and capacitive reactance calculator provide component-level analysis for AC circuit design.
AC voltage and current are sinusoidal — they continuously vary between positive and negative peaks. The RMS (Root Mean Square) values are the equivalent DC values that would produce the same power dissipation in a resistive load. For a sinusoidal waveform: V_RMS = V_peak / √2 ≈ 0.707 × V_peak. Standard household voltages (120V in North America, 230V in Europe) are already RMS values. Always use RMS values — not peak values — in power calculations. The AC circuit calculators category includes three-phase power, delta-wye conversion, and frequency tools for complete AC system analysis.
The AC wattage calculator uses the fundamental AC power relationships based on the power triangle:
Apparent Power:
$$S = V_{rms} \times I_{rms}$$
where S is measured in volt-amperes (VA).
Real Power:
$$P = V_{rms} \times I_{rms} \times \cos\varphi = S \times PF$$
where P is measured in watts (W) and PF is the power factor (cos φ).
Reactive Power:
$$Q = \sqrt{S^2 - P^2}$$
or equivalently $$Q = S \times \sin\varphi$$, measured in volt-amperes reactive (VAR).
Phase Angle:
$$\varphi = \arccos(PF)$$
The phase angle represents the angular displacement between the voltage and current waveforms. For a purely resistive load, φ = 0° and PF = 1. For a purely reactive load, φ = 90° and PF = 0.
The results display the complete power breakdown of the AC circuit. Real power indicates the useful energy being consumed. Apparent power represents what the source must deliver, and it determines equipment sizing. Reactive power shows the non-productive power component. A large reactive power relative to real power indicates a low power factor, suggesting the circuit has significant inductive or capacitive loading. The phase angle quantifies this displacement—larger angles mean more reactive power and less efficient power delivery.
Inputs
Results
A 240V air conditioner drawing 8A with a power factor of 0.85 consumes 1632W of real power. The apparent power is 1920 VA, and approximately 1012 VAR of reactive power oscillates in the circuit.
Inputs
Results
A 480V industrial motor drawing 25A with a power factor of 0.75 consumes 9 kW of real power but requires 12 kVA of apparent power. The 7937 VAR of reactive power indicates the motor has a significant inductive component.
Real power (measured in watts) is the actual energy consumed by the load and converted into useful work or heat. Apparent power (measured in volt-amperes) is the total power that the source must supply, including both the real and reactive components. The ratio of real power to apparent power is the power factor. In a purely resistive circuit, they are equal; in circuits with inductors or capacitors, apparent power exceeds real power.
Reactive power is the power that oscillates back and forth between the source and reactive components (inductors and capacitors) without performing useful work. It matters because it increases the total current flowing through the system, causing additional losses in wires and transformers, and reduces the available capacity for delivering real power. Utilities often charge penalties for excessive reactive power consumption.
A power factor of 0.95 or higher is generally considered excellent. Most utilities require industrial customers to maintain a power factor above 0.90 to avoid penalties. Residential loads typically have power factors between 0.80 and 0.95. A power factor of 1.0 (unity) is ideal and means all power delivered is real power, but this is rarely achieved in practice with inductive loads.
The most common method is to add capacitor banks in parallel with inductive loads (such as motors) to offset the lagging reactive power. Other methods include using synchronous motors or synchronous condensers, installing active power factor correction (PFC) circuits in electronic equipment, and avoiding running motors at less than full load where power factor drops significantly.
RMS stands for Root Mean Square. It is the effective value of an AC waveform that produces the same heating effect as an equivalent DC value. For a sinusoidal waveform, the RMS value is the peak value divided by √2 (approximately 0.707 times the peak). When we say household voltage is 120V or 240V, we are referring to the RMS value, not the peak value.
No, the power factor is defined as the cosine of the phase angle between voltage and current, and cosine values range from 0 to 1 (considering magnitude). A power factor greater than 1 would violate the fundamental relationship S² = P² + Q² in the power triangle. If a measurement yields a value above 1, it indicates a measurement error or non-sinusoidal waveform requiring harmonic analysis.
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