Single-Phase Power Calculator

Estimate apparent power, real input power, and useful output power for a single-phase AC load.

RMS voltageNumber from 0.001 to 1000000 V.RMS currentNumber from 0 to 1000000 A.Power factorNumber from 0 to 1.EfficiencyNumber from 0.1 to 100 %.

Use the units shown beside each field. Decimal and scientific notation are accepted for non-integer fields; blanks, commas, fractions and non-finite entries are rejected.

Calculate

Apparent power4800 VA

Real input power4320 W

Useful output power3974.4 W

Real input power4.32 kW

The displayed results apply to the default example. Enable JavaScript to calculate other inputs.

How to use this calculator

1. Replace the example values with measurements or ratings for the exact vehicle, circuit, component or system.
2. Keep every value in the labeled unit and use manufacturer data where available.
3. Select Calculate, then review the result together with the limitations and safety notes.

Formula and method

Apparent power S = V × I. Real power P = S × power factor. Useful output = real input × efficiency.

Calculations run in your browser. Results are hidden whenever an input changes or validation fails, preventing an older result from being mistaken for a new calculation.

Worked example

RMS voltage = 240 V; RMS current = 20 A; Power factor = 0.9; Efficiency = 92 %. The calculator returns Apparent power = 4800 VA; Real input power = 4320 W; Useful output power = 3974.4 W; Real input power = 4.32 kW.

The worked example uses the same defaults shown in the interface, allowing the formula and displayed result to be checked together.

Limitations and safety

This is a steady-state sinusoidal estimate. Harmonics, starting current, waveform distortion, duty cycle and code requirements are not included.

This is an educational planning model. Confirm ratings, tolerances, code requirements and safe procedures with manufacturers and qualified professionals before purchasing, modifying, wiring or operating equipment.

Frequently asked questions

Why are VA and watts different?

VA is apparent power; watts are the portion doing average real work. Power factor relates the two.

Why does the calculator reject my entry?

Each field shows its supported range. Whole-number fields reject decimals, and all fields reject blanks, words, comma-formatted numbers, fractions and non-finite values.

How should I use the displayed precision?

Keep extra digits while checking the calculation, then round to the precision supported by the measurements, component tolerances and published ratings.

Review notes and reference

Reviewed October 4, 2026. The formula and default example were checked together. The script was tested for defaults, input boundaries, invalid formats, condition-specific errors and recovery after an error. Reference: OSHA electrical safe-work requirements. Explanations and examples are original.

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