Heat of Combustion Calculator
Enter the amount of substance combusted and the molar heat of combustion (from a reference table or measurement) to calculate the total enthalpy change. A negative value means heat is released (exothermic), matching standard thermochemical sign convention.
Last updated: September 26, 2026
Frequently asked questions
What is heat of combustion?
It's the enthalpy change when a specified amount of a substance is completely combusted, usually reported per mole (molar heat of combustion). It's typically negative, since combustion releases heat.
Why is the value negative?
By thermochemical convention, a negative enthalpy change means the system releases energy to its surroundings (exothermic). Combustion reactions are exothermic, so their heats of combustion are conventionally negative.
Where do I get the molar heat of combustion?
From a reference table (such as a chemistry handbook) or from calorimetry data. This calculator doesn't include built-in fuel values - you supply the number for the specific substance and conditions you're working with.
How is this different from the Combustion Reaction Calculator?
The Combustion Reaction Calculator (part of the Chemical Equation Balancer) balances the symbolic chemical equation for combustion. This calculator instead computes the total energy released or absorbed from an amount of substance and a known molar enthalpy value - it doesn't balance equations.
How is this different from Combustion Analysis?
Combustion Analysis works backward from measured CO2 and H2O masses to find a sample's elemental composition. This calculator instead uses a known molar heat of combustion to find total energy, and doesn't analyze elemental composition.
Does this tell me how to safely burn something?
No. It performs thermochemical arithmetic only, using values you already have. It includes no guidance on combustion apparatus, fuel handling, ignition, or safety procedures.