Efficiency Calculator

Compute efficiency (%), losses (W), and output/input power using either Power mode or V×I mode.

How to Use

  1. Pick a mode: Power (Pin/Pout) or V×I (Vin/Iin and Vout/Iout).
  2. Enter known values. The tool computes efficiency and losses instantly.
  3. Use “Solve For” to force a target output (Efficiency, Pin, Pout, or Loss).
  4. Open “Show Work” for formulas and step-by-step calculations.
Efficiency Meter
Outputs update live. Work is shown in base units (V, A, W).
η
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Pin
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Pout
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Loss
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Heat Risk: —
Inputs & Settings
Choose a mode, then enter values. The tool computes η, power, and losses.
Optional input. If blank, η is computed from power.
Power mode only. In V×I mode, Pin = Vin × Iin.
Power mode only. In V×I mode, Pout = Vout × Iout.
Optional input. Ploss = Pin − Pout (if both known).
V×I mode only.
V×I mode only.
V×I mode only.
V×I mode only.
Show Work (step-by-step)
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Work is shown in base units (W, V, A). Percent is shown as η × 100.

Efficiency Formulas

Efficiency: η = Pout ÷ Pin (dimensionless), or η% = (Pout ÷ Pin) × 100.

  • Loss / heat: Ploss = Pin − Pout
  • Power from V×I: P = V × I
  • Output from efficiency: Pout = η × Pin
  • Input from efficiency: Pin = Pout ÷ η
Where Pin is input power, Pout is output power, and η is efficiency (0–1).

FAQ

Why can Pout be higher voltage but lower current?

In DC-DC converters, voltage and current trade off. Ideally Pin ≈ Pout, but in reality Pin > Pout due to losses.

What does “loss” represent?

Loss is the power not delivered to the load—usually heat in semiconductors, magnetics, and wiring: Ploss = Pin − Pout.

Can efficiency be over 100%?

Not for a passive converter. If calculations show >100%, it usually means mismatched measurements, wrong units, or ripple/measurement error.

Do AC or power factor matter here?

This tool is for basic electrical efficiency using real power (watts). For AC with power factor, use true power (W), not VA.

Tool Info

Last updated:

Updates may include unit support, converter workflows, and edge-case handling.