Heat Engine Efficiency Calculator

How it is calculated

The tool computes the Carnot efficiency η = (1 − Tc / Th) × 100. You type the hot and cold reservoir temperatures in degrees Celsius; the tool first converts them to kelvin with T(K) = T(°C) + 273.15, because the ratio only works on the absolute scale. Th is the hot-side temperature, Tc the cold-side temperature, and the result is a percentage rounded to two decimals.

There is no result if the hot temperature is not higher than the cold one, or if either temperature is below absolute zero (−273.15 °C). The figure is an upper limit set by thermodynamics, not the efficiency of a real engine, which is always lower.

Common mistakes

• Using Celsius values directly in the ratio by hand (30 / 500); the formula needs kelvin, and the tool adds 273.15 for you, so do not type kelvin values into the Celsius fields.
• Swapping the hot and cold temperatures; the tool then returns nothing because the hot side must be warmer.
• Treating the result as the efficiency a real plant or engine will reach; friction, heat loss and combustion limits push real values well below the Carnot figure.
• Entering the gas or flame temperature of a combustion engine as the hot reservoir when the working fluid actually sees a much lower average temperature.
• Using this for refrigerators or heat pumps; their performance is described by a coefficient of performance, not by this efficiency.