Heat Engine Efficiency Calculator

About this calculator

The Carnot efficiency formula η = 1 − Tc/Th (temperatures in Kelvin) gives the theoretical maximum efficiency any heat engine can achieve while operating between a hot reservoir at Th and a cold reservoir at Tc. This limit comes directly from the second law of thermodynamics — no real engine, no matter how well engineered, can exceed it, and every real engine falls further below it due to friction, heat loss, and other irreversibilities.

Mechanical and thermal engineers use this ceiling to benchmark real power plants, internal combustion engines, and refrigeration cycles (which apply the same relationship in reverse) against the best physically possible performance for their operating temperatures. Physics students meet it as the canonical illustration of why perpetual-motion or 100%-efficient engines are impossible.