The Efficiency Calculator finds what fraction of the energy or power supplied to a machine, motor, or engine comes out as useful work, expressed as a simple percentage. It's the same concept engineers use to compare motors, appliances, and power systems — more efficient means less waste for the same input.
How the Efficiency Calculator works
The calculator applies η = output/input × 100, where output is the useful energy or power a system delivers and input is the total energy or power supplied to it. Both must be in the same unit — joules (J) for a fixed amount of energy, or watts (W) for a rate of power — since efficiency is a dimensionless ratio and mixing units gives a meaningless number.
Once efficiency is known, the calculator can also work backward: given a target efficiency and either the output or the input, it solves for the missing value. And on the Loss tab, it reports the energy or power that did not become useful output (loss = input − output), which is where design and maintenance improvements usually focus.
Inputs and what they mean
Useful output is the energy or power that actually does the job you care about — the mechanical work an electric motor produces, the light from a bulb, or the heat delivered by a furnace. Total input is everything supplied to the system, including the part that gets wasted. For a well-designed electric motor, efficiency often runs 85-95%; a typical incandescent bulb converts only about 5-10% of its electrical input into visible light, with the rest lost as heat — which is exactly why efficiency numbers matter for choosing equipment.
Choose the unit (J or W) that matches how your output and input were measured — it's a label only, not a converter, so make sure both numbers already share that unit before entering them.
Limits and edge cases
Efficiency can never legitimately exceed 100% — that would mean a machine produces more useful output than the energy it was given, which violates conservation of energy. If this calculator shows an over-100% result, it means output and input were entered backward, measured in different units, or one of the values is simply wrong; it will flag this rather than show a false percentage. A total input of zero is also undefined (there's nothing to compute a ratio against), so the calculator requires a positive, non-zero input. This calculator reports the real, measured efficiency from your numbers — for the theoretical maximum efficiency a heat engine could ever achieve based on temperature alone, see the Carnot Efficiency Calculator instead.