Efficiency Calculator (η = Output / Input × 100%)

What efficiency really measures

Efficiency tells you how much of the energy or power you put into a system actually comes out as useful work. The rest is lost, usually as heat, sometimes as noise or vibration. The formula is short:

η = (useful output / total input) × 100%

Output and input have to be in the same units. Joules in and joules out, or watts in and watts out. Time cancels, so an energy ratio and a power ratio give the same percentage. Efficiency (η, the Greek letter eta) can never exceed 100%, because the first law of thermodynamics says no more energy comes out than went in.

A motor example

An electric motor that draws 500 watts and delivers 400 watts of mechanical power runs at 400 / 500 = 0.80, or 80% efficient. The missing 100 watts heats the windings. Good industrial motors do far better, often 90 to 97%, which is one reason electric drivetrains beat combustion engines on raw energy use.

Why no heat engine hits 100%

Some losses are sloppy engineering you can fix. Others are baked into physics. Any engine that turns heat into work is capped by the Carnot limit:

η_max = (1 - T_cold / T_hot) × 100%

with both temperatures in kelvin. A power plant running steam at 800 K and rejecting heat at 300 K cannot beat 1 - 300/800 = 62.5%, no matter how clever the design. Real plants land well under that. Enter the hot and cold temperatures below and this calculator works out the Carnot ceiling for you, then tells you what fraction of that ceiling your system actually reaches.

Losses multiply in a chain

When power flows through several stages you multiply the efficiencies, you do not average them. A generator at 90%, a transmission line at 95%, and a motor at 90% give 0.90 × 0.95 × 0.90 = 0.77. Three respectable stages, and nearly a quarter of the energy is gone before it does anything useful. That compounding is why engineers fight for a single percentage point in large systems.

Where it shows up

Solar panels (15 to 22% for silicon), LED bulbs (roughly 35 to 50% against about 5% for the old incandescents), gearboxes, pumps, refrigerators, and whole factories all get rated this way. Lifting efficiency a few points across a power grid or a vehicle fleet saves real fuel and money, which is why it is one of the most quoted numbers in engineering.