AC Wattage Calculator — Real, Apparent & Reactive Power
Enter the RMS voltage, current, power factor and phase type to compute real power (watts), apparent power (VA), reactive power (VAR) and the power factor angle for any AC circuit.
V
A
Phase
Actual power consumed and converted to work or heat
- 1
Apparent power (single-phase)
230 × 5 = 1,150 VA - 2
Real power
1,150 × 0.85 = 977.50Power factor (cos φ) converts apparent power to the portion that does useful work.
How does this calculator work?
Real power P (W) = V × I × PF (single-phase) or √3 × V × I × PF (three-phase). Apparent power S (VA) = V × I. Reactive power Q (VAR) = S × √(1 − PF²). Enter RMS voltage, current and power factor to get all three power values and the phase angle.
Formula
How this is calculated
In an AC circuit, voltage and current are sinusoidal — they can be out of phase with each other due to inductance (motors, transformers) or capacitance. Three power quantities describe this situation. Apparent power S (in VA) = V × I is the simple product of RMS voltage and RMS current. Real (active) power P (in W) = S × PF is what actually does work or generates heat. Reactive power Q (in VAR) = S × √(1 − PF²) is the portion stored and returned by reactive elements each cycle — it does no net work but must still be supplied by the source.
The power factor PF = cos(φ) is the cosine of the phase angle φ between voltage and current. PF = 1 means the load is purely resistive (voltage and current are in phase); PF = 0 means purely reactive. Most motors and compressors operate between 0.7 and 0.95. Utilities often charge industrial customers for low power factor because high reactive power increases current and line losses without doing useful work.
For three-phase circuits, both formulas multiply by √3 ≈ 1.732, which accounts for the three phases adding in a balanced system. The voltage entered should be the line-to-line (phase-to-phase) RMS voltage, as labelled on most three-phase equipment nameplates.
Frequently asked questions
Watts (W) measure real power — energy converted to useful work or heat per second. Volt-amperes (VA) measure apparent power — the total current-voltage product including the reactive component that flows back and forth. VA ≥ W always; they are equal only when PF = 1.
Resistive loads (heaters, incandescent bulbs) have PF ≈ 1. Single-phase induction motors (fans, compressors) are typically PF 0.7–0.9 depending on load. LED drivers often have PF 0.5–0.95; switched-mode power supplies (computers, chargers) range 0.6–0.99 depending on whether they have PFC correction.
Multiply apparent power (kVA) by the power factor: kW = kVA × PF. For example, a 10 kVA generator with a 0.8 PF load delivers 8 kW of real power.
TG we-Calculate Editorial Team. (2026). AC Wattage Calculator — Real, Apparent & Reactive Power [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/ac-wattage-calculator
TG we-Calculate Editorial Team. "AC Wattage Calculator — Real, Apparent & Reactive Power." TG we-Calculate. 2026. https://we-calculate.com/calculator/ac-wattage-calculator.
TG we-Calculate Editorial Team, "AC Wattage Calculator — Real, Apparent & Reactive Power," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/ac-wattage-calculator
@misc{wecalculate_ac_wattage_calculator, title = {AC Wattage Calculator — Real, Apparent & Reactive Power}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/ac-wattage-calculator}}, year = {2026}, note = {TG we-Calculate} }
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