Fuel Energy Content Calculator

Fuel energy content measures how much chemical energy is stored in a given quantity of fuel. This directly determines how far a vehicle can travel, how long a generator will run, or how much heat a furnace can produce.

Energy content formula:

Total Energy = Volume × Energy Density

Useful Energy = Total Energy × Thermal Efficiency

Two numbers per fuel, and they are not the same

Burn any hydrocarbon and some of the hydrogen in it becomes water vapour. The higher heating value counts the energy you would get back by condensing that vapour; the lower heating value does not. An engine sends the vapour straight out the exhaust pipe hot, so the LHV is what it can actually deliver, and that is what the table and the calculator below use for the liquid fuels.

Hydrogen shows the difference at its most extreme, because it produces nothing but water: 120 MJ/kg lower against 142 MJ/kg higher. Ordinary liquid fuels carry far less hydrogen and the gap is correspondingly small. It still matters in one place you will meet it, though: a condensing boiler recovers part of that latent heat, which is why they get quoted at over 100% efficiency. They are measured against the lower value.

Energy density of common fuels:

The natural-gas rows are worth a second look. Per kilogram it beats every liquid fuel on the list, but a gas has almost no mass in a given volume, so per litre of tank it loses badly even squeezed to 250 bar. That is why compressed-gas vehicles carry such enormous tanks. Liquefying it doubles the density again, at the cost of keeping it at −162 °C. One caveat on that 1,037 BTU per cubic foot: it is the gross figure your gas utility bills by, so it is the one row here that is a higher heating value.

Thermal efficiency of common engines:

Worked example: A diesel truck has a 150-liter tank. How far can it travel?

• Total energy: 150 L × 38.3 MJ/L = 5,744 MJ
• Useful energy (40% efficiency): 5,744 × 0.40 = 2,298 MJ
• Assume fuel economy of 8 L/100 km:
  • Range = 150 ÷ 8 × 100 = 1,875 km per tank

Why efficiency matters so much: Even at 40% efficiency, 60% of the diesel’s energy leaves as heat. That is why engine cooling systems are so large, and why a truck radiator is the size it is. Electric vehicles convert over 85% of stored energy into motion, which is a different problem entirely: their limit is how much energy the battery holds, not how much of it survives the conversion.