Thermal Efficiency Calculator

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

About Thermal Efficiency Calculator

Thermal efficiency is net work divided by heat supplied. 350 kJ of work from 1000 kJ of heat is 35% efficient, rejecting 650 kJ. Power engineers often quote the reciprocal as heat rate: 35% corresponds to 10,286 kJ per kWh, and the theoretical floor is 3600 kJ/kWh at 100% efficiency.

Formulas

Thermal efficiency

efficiency = W(net) / Q(in)

Heat rate

heat rate = 3600 / efficiency in kJ/kWh

Worked example

With the default values below, Thermal Efficiency Calculator returns Thermal Efficiency of 35.00%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Net work outputminimum 0 kJ: 350 kJ
Heat suppliedminimum 0 kJ: 1,000 kJ

Results

Thermal Efficiency: 35.00%
Heat Rejected: 650.000 kJ
Heat Rate: 10,285.7 kJ/kWh
Heat Input Per Unit Of Work: 2.8571

Step by step

1Values used
2Thermal efficiency
3Heat rate
4Thermal Efficiency= 35.00
5Heat Rejected= 650.000 kJ
6Heat Rate= 10,285.7 kJ/kWh
7Heat Input Per Unit Of Work= 2.8571

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

What efficiencies do real plants reach?

About 35-40% for a coal steam plant, 40% for a large diesel, and up to 62% for a combined cycle gas turbine.

Why is heat rate used instead of efficiency?

Because fuel is bought by energy content. Heat rate reads directly as fuel consumed per unit of electricity sold.