Efficiency Calculator

What Is Efficiency?

Efficiency measures how much of the input energy or power is converted into useful output. No real machine reaches 100% because friction, heat, and other losses always consume part of the input.

Efficiency Formula

$$\eta = \frac{\text{output}}{\text{input}} \times 100\%$$

Output and input must be in the same units — joules, watts, or any consistent energy measure. Example: 80 J useful work from 100 J input gives $\eta = 80\%$.

Energy Loss

Wasted energy is simply input minus output. A 80% efficient motor fed 1000 W delivers 800 W of useful power and dissipates 200 W as heat and other losses.

Frequently Asked Questions

Can efficiency be over 100%?

No for a single conversion step. Efficiency above 100% would violate conservation of energy. Heat pumps move heat rather than create it, so their COP can exceed 1, but that is a different metric.

Do output and input need the same units?

Yes. Compare like with like: joules to joules, watts to watts, or horsepower to horsepower.

What is a typical motor efficiency?

Modern electric motors often reach 85–95% efficiency at rated load. Internal combustion engines are typically 20–40% thermally efficient.

How is this different from Carnot efficiency?

This is actual measured efficiency. Carnot efficiency is the theoretical maximum for a heat engine between two temperatures.

What if output exceeds input?

Check your measurements. True efficiency above 100% indicates an error, unless you are using a different definition such as heat pump COP.

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What Is Efficiency?

Efficiency Formula

Energy Loss

Frequently Asked Questions

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