AC Wattage Calculator
Real power (W), apparent power (VA), reactive power (VAR) and power factor — solve any missing variable, do 3-phase math, and size PF-correction capacitors. 100% client-side.
AC Power Solver (single-phase)
Enter any three values — the solver finds the fourth and completes the power triangle.
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Example: 230 V × 10 A × PF 0.8 → P = 1840 W, S = 2300 VA, Q = 1380 VAR, φ = 36.87°. Formulas: P = V×I×PF, S = V×I, Q = √(S²−P²).
Three-Phase Power
P = √3 × Vline-to-line × I × PF. Enter any three — solve the fourth.
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Example: 400 VLL × 10 A × PF 0.85 → P = 5888.97 W, S = 6928.20 VA, Q = 3649.66 VAR.
Power Factor Correction
Size the capacitor bank needed to lift power factor from PF₁ to PF₂: Qc = P × (tan φ₁ − tan φ₂).
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Example: 1840 W from PF 0.8 → 0.95 at 230 V / 50 Hz needs 775.22 VAR of capacitance ≈ 46.65 µF. 3-phase values are per phase.
| Load type | Typical PF (guidance only) |
|---|---|
| Induction motor | 0.7 – 0.9 |
| LED lighting | ≈ 0.9 |
| Laptop / phone charger (no PFC) | 0.5 – 0.7 |
| Heater, kettle, incandescent | 1.0 |
Typical values are a rough guide, not specifications — measure or use the most pessimistic value for critical sizing.
Use a different tool when…
- You only need W ↔ VA conversion (no V/I math) → watts-to-VA converter
- You are sizing a PC power supply or estimating appliance energy cost → wattage calculator
- You need general electrical unit conversion (V, A, Ω, prefixes) → electrical unit converter
AC Power FAQ
What is the difference between watts and VA in AC power?
Real power (watts) is what does useful work; apparent power (VA) is what the wiring, breakers, and generator must carry. They are related by power factor: P = V x I x PF, S = V x I. Example: 230 V x 10 A x PF 0.8 = 1840 W of real power, but 2300 VA of apparent power — the leftover 1380 VAR sloshes back and forth as reactive power. Size equipment for VA, pay for watts.
How do I calculate AC wattage from volts and amps?
P = V x I x power factor. Multiply voltage, current, and power factor. Example: 230 V x 10 A x 0.8 = 1840 W. Apparent power is just S = V x I = 2300 VA, and reactive power is Q = sqrt(S^2 - P^2) = sqrt(2300^2 - 1840^2) = 1380 VAR. The solver tab above does all of this and also works backwards.
Can the calculator solve for power factor if I know watts, volts, and amps?
Yes — enter any three of power, voltage, current, and power factor, and the solver finds the fourth. For example, enter P = 1840 W, V = 230 V, I = 10 A, and it solves PF = 1840 / (230 x 10) = 0.80, plus S = 2300 VA and Q = 1380 VAR automatically.
How do you calculate 3-phase AC power?
Three-phase real power is P = sqrt(3) x V_line-to-line x I x PF. Example: a 400 V line-to-line motor drawing 10 A at PF 0.85 delivers 1.732 x 400 x 10 x 0.85 = 5888.97 W, with 6928.20 VA apparent and 3649.66 VAR reactive. The 3-phase tab solves any missing variable the same way.
How do I size a capacitor for power factor correction?
Use Qc = P x (tan(phi1) - tan(phi2)): the reactive power to cancel. Example: an 1840 W load at PF 0.8 corrected to 0.95 needs 1840 x (tan(36.87 deg) - tan(18.19 deg)) = 1840 x (0.75 - 0.3287) = 775.22 VAR of capacitance. At 230 V / 50 Hz that is C = Qc / (2 x pi x 50 x 230^2) = 46.65 uF. The correction tab computes this for 1-phase and 3-phase (delta or star).
What is a typical power factor for a motor?
As a rough guide only: induction motors typically 0.7-0.9, LED lighting around 0.9, laptop/phone chargers 0.5-0.7 without PFC, heaters and kettles 1.0. These are TYPICAL values, not specifications — actual power factor varies with load and design. For sizing critical equipment, measure or use the most pessimistic value.
Can power factor be greater than 1?
Because PF = P / S can never exceed 1, apparent power is always at least as large as real power. A power factor above 1 is physically impossible (it would mean more useful work than total power delivered) — this calculator rejects PF > 1 as invalid input instead of computing nonsense.
Does this calculator work for non-linear loads like VFDs?
This tool assumes steady-state sinusoidal AC — the classic power-triangle math. It does not model non-linear loads (variable-speed drives, cheap switch-mode supplies without PFC) where harmonic distortion makes 'PF' more complicated than cos(phi). For those, a true-RMS power meter is the honest instrument.
What is the difference between kVA and kW, and which related tools should I use?
kVA is apparent power (what equipment must carry); kW is real power (what does work). They differ by power factor: kW = kVA x PF. A 10 kVA generator at 0.8 PF delivers 8 kW. For a plain W-to-VA conversion, use our watts-to-VA converter; for general electrical units, the electrical unit converter; for PC power supplies and appliance energy cost, the wattage calculator.
Honest scope: this tool assumes steady-state sinusoidal AC (classic power-triangle math). It does not model non-linear loads (VFDs, cheap switch-mode supplies) where harmonics make power factor more complex than cos φ — use a true-RMS power meter there. Results are estimates for planning, not a substitute for a licensed electrician on real installations.
Free tool by NRTechStudio