Carnot Efficiency Calculator

Work out carnot efficiency instantly with clear inputs, formula shown and shareable results.

About Carnot Efficiency Calculator

No heat engine between two reservoirs can beat 1 - Tc/Th, and only a reversible one reaches it. Between 800 K and 300 K the ceiling is 62.5%, so 625 J of every kilojoule could become work and at least 375 J must be rejected. Real engines fall well short - a modern gas turbine reaches about 40%.

Formulas

Carnot efficiency

efficiency = 1 - Tc / Th, temperatures in kelvin

Rejected heat

Q(cold) = Q(hot) x Tc / Th

Worked example

With the default values below, Carnot Efficiency Calculator returns Carnot Efficiency of 62.50%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Hot reservoir temperatureminimum 0 K: 800 K
Cold reservoir temperatureminimum 0 K: 300 K

Results

Carnot Efficiency: 62.50%
Work From Each Kilojoule Of Heat: 625.0 J
Cold-To-Hot Temperature Ratio: 0.3750
Heat Rejected Per Kilojoule Supplied: 375.0 J

Step by step

1Values used
2Carnot efficiency
3Rejected heat
4Carnot Efficiency= 62.50
5Work From Each Kilojoule Of Heat= 625.0 J
6Cold-To-Hot Temperature Ratio= 0.3750
7Heat Rejected Per Kilojoule Supplied= 375.0 J

Assumptions and limits

The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why can't a real engine reach Carnot efficiency?

Because it requires infinitely slow, frictionless, fully reversible operation. Any finite power output means irreversibility and lost work.

How do I improve efficiency?

Raise the hot temperature or lower the cold one. Materials limit the first, ambient conditions the second, which is why combined cycles chase every extra degree.