Heat of Combustion Calculator
Calculate the heat released when burning fuels.
Choose from methane, ethanol, propane, octane, hydrogen, or enter a custom combustion enthalpy.
The heat of combustion (ΔH_combustion) is the enthalpy change when one mole of a substance burns completely in excess oxygen under standard conditions (25°C, 1 atm).
Formula:
q = |ΔH_c| × n
where n = moles of fuel burned.
Standard heats of combustion (higher heating values, liquid water product):
| Fuel | Molar Mass (g/mol) | ΔH_c (kJ/mol) | Energy/g (kJ/g) |
|---|---|---|---|
| Hydrogen (H₂) | 2.016 | −285.8 | −141.8 |
| Methane (CH₄) | 16.04 | −890.4 | −55.5 |
| Ethanol (C₂H₅OH) | 46.07 | −1366.8 | −29.7 |
| Propane (C₃H₈) | 44.10 | −2220.0 | −50.3 |
| Butane (C₄H₁₀) | 58.12 | −2877.5 | −49.5 |
| Octane (C₈H₁₈) | 114.2 | −5471.0 | −47.9 |
| Carbon (graphite) | 12.01 | −393.5 | −32.8 |
| Glucose (C₆H₁₂O₆) | 180.2 | −2803.0 | −15.6 |
Higher vs Lower Heating Value:
- Higher (HHV): water product is liquid — more heat released
- Lower (LHV): water product is gas — accounts for vaporization energy
Real-world energy comparison:
- 1 kg methane ≈ 55.5 MJ (LNG fuel)
- 1 kg gasoline (octane equivalent) ≈ 47.9 MJ
- 1 kg wood (dry) ≈ 15-18 MJ
- 1 kg TNT (explosive equivalent) ≈ 4.6 MJ
- 1 kg hydrogen ≈ 141.8 MJ (highest energy density by mass of any fuel)
Worked example
Burn 50 g of propane (molar mass 44.10 g/mol, ΔH_c = 2,220 kJ/mol):
moles = 50 ÷ 44.10 = 1.134 mol heat released = 1.134 × 2,220 = 2,517 kJ
That is roughly enough to bring 7.5 litres of water from room temperature to the boil, and it is why a small camping canister goes a long way.
Higher and lower heating value
Combustion enthalpies come in two flavours and the gap between them is not trivial. The higher heating value counts the heat you would get back if the water vapour in the exhaust condensed to liquid. The lower heating value does not, because in most real equipment that vapour disappears up the flue still as steam, carrying its latent heat with it.
For methane the two differ by about 11%. Domestic gas is billed on the higher value, since a modern condensing boiler genuinely does recover much of that latent heat. Engine and turbine work quotes the lower value, because nothing in an exhaust pipe is going to condense. Comparing a figure from one convention against a figure from the other is a common way to end up with an efficiency above 100%, which is always a sign that the two numbers came from different books.
Sign conventions
Combustion enthalpies are tabulated as negative, because the system loses energy. This calculator asks for the magnitude and reports heat released as a positive number, which is what you want when the question is “how much heat do I get”. If you are writing a thermodynamic equation rather than sizing a burner, put the minus sign back.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.