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Heat of Combustion Calculator – Easily calculate the higher heating value of fuels in MJ/kg or kJ/mol with formula, steps and instant result.
The heat of combustion is one of the most fundamental values in both chemistry and physics. It tells us how much energy a fuel can release when it completely burns in oxygen. It helps engineers, researchers, fuel manufacturers, and even car owners compare fuels like diesel, gasoline, ethanol or natural gas. That is why we built an advanced yet easy to use Heat of Combustion Calculator, so everyone can calculate fuel energy release with simple inputs and step-by-step results.
Our Heat of Combustion Calculator works on the principle of the higher heating value. It takes the lower heating value, adds the heat used to form water vapor and gives a final result that is extremely useful in real world fuel analysis. Instead of doing heavy physics calculations manually, our calculator works instantly. Whether you are comparing diesel and gasoline or calculating molar heat of combustion in kJ/mol for exam purpose, you get accurate results in seconds.
The heat of combustion is defined as the total energy released when one mole or one kilogram of a fuel completely reacts with oxygen. It is often expressed either in MJ/kg or in kJ/mol. This is why it is sometimes called higher calorific value or higher heating value. When fuel burns, water vapor is produced. The formula for heat of combustion considers even that vaporization energy:
Hc = LHV + Hv × (moles of H₂O / moles of fuel)
In simple terms, take the lower heating value of the fuel, add the heat of vaporization multiplied by the ratio of water moles released. The result is the higher heating value, which gives you the actual energy content of the fuel.
To manually calculate heat of combustion in physics chemistry or engineering, follow this simple process. First note the LHV value of the fuel. Then note the heat of vaporization of water. Measure how many moles of water vapor are released and how many moles of fuel is combusted. Divide the water moles by fuel moles. Multiply the ratio by Hv and then add the result to the lower heating value. The final number is the heat of combustion in the same unit.
Many students also ask how to calculate heat of combustion in kJ/mol. You use the same formula, only keep the units in kJ and per mole. If LHV is in kJ/mol, Hv must also be in kJ/mol.
The molar heat of combustion simply means the heat of combustion per mole of fuel. The same formula, written in molar form, looks like this:
Hc (kJ/mol) = LHV (kJ/mol) + Hv (kJ/mol) × (nH₂O / nfuel)
That is the exact same formula used in your car fuel combustion calculations, diesel efficiency test, and even Excel models. So whether you use an Excel heat of combustion calculator or a chemical physics calculator, the math remains the same.
You can use our Heat of Combustion Calculator very easily. Just enter the lower heating value of your fuel. Type or select the heat of vaporization of water. Enter how many moles of water vapor are released and how many moles of fuel is burned. Press calculate. Our system instantly shows the heat of combustion and even shows each calculation step in clear text so you can learn how it was done. This calculator can be used for methane, ethanol, diesel, gasoline, natural gas, hydrogen and more. You can even calculate the heat of combustion of ethanol 100, or check the energy released in your car fuel.
Understanding the heat of combustion is extremely important in fuel comparison and thermal physics. From diesel engines to power plants and laboratory analysis, this value tells us how much real usable energy is stored in a chemical fuel. Our Heat of Combustion Calculator simplifies all of this with a professional formula, easy steps, and accurate results. Students, physics teachers, engineers, and even motor enthusiasts can benefit from this. Whether you need to know how to calculate heat of combustion in kJ/mol, in MJ/kg or even when building an Excel sheet, now you can do it instantly and correctly.
It is equal to the lower heating value plus the vaporization heat of water multiplied by the number of water moles produced per mole of fuel. It follows the basic law of energy conservation.
Each gas has a unique heat of combustion. For example, methane releases about 55.5 MJ/kg while natural gas varies depending on composition. Our calculator can show you the exact number.
Hc (kJ/mol) = LHV (kJ/mol) + Hv (kJ/mol) × (moles of water / moles of fuel)
Pure ethanol has a heat of combustion of about 26.8 MJ/kg. You can enter its LHV into the calculator and get the final higher heating value.
Use the same formula but enter all values in kJ and per mole. Divide moles of water vapor by moles of fuel, multiply by Hv (kJ/mol) and add to LHV in kJ/mol.