Maximum Theoretical Efficiency Calculator

About this calculator

The Carnot efficiency is the absolute upper limit the second law of thermodynamics allows for any heat engine operating between a hot reservoir at temperature Th and a cold reservoir at temperature Tc, both measured in kelvin: η = 1 − Tc/Th. It comes from the idealized Carnot cycle — a reversible sequence of isothermal and adiabatic expansions/compressions — and depends only on the two temperatures, never on the working fluid or the machinery involved.

No real engine reaches this figure because real cycles involve friction, finite-rate heat transfer, and other irreversibilities, but the Carnot limit is exactly why raising the hot-side temperature (or lowering the cold sink) is the standard lever engineers pull to squeeze more work out of power plants, jet engines and internal-combustion engines. It is also the benchmark used to judge how far a real thermodynamic cycle falls short of the theoretical maximum. This calculator plugs your two reservoir temperatures directly into 1 − Tc/Th.