Fuel Energy Content Calculator
Calculate the energy content of gasoline, diesel, natural gas, or propane in BTU and kilojoules.
Compare fuel types by energy density.
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
Energy density of common fuels:
| Fuel | MJ/Liter | MJ/kg | BTU/gallon |
|---|---|---|---|
| Gasoline | 34.2 | 46.4 | 124,300 |
| Diesel | 38.6 | 45.4 | 139,000 |
| Ethanol (E100) | 21.2 | 26.8 | 76,100 |
| E10 (10% ethanol) | 33.2 | — | 120,900 |
| LPG (propane) | 25.5 | 49.6 | 91,300 |
| CNG (natural gas) | 22.2 | 53.6 | 20,160/ft³ |
| Hydrogen | 10.0 | 142.0 | 51,500/kg |
Thermal efficiency of common engines:
| Engine Type | Efficiency |
|---|---|
| Gasoline engine | 20–35% |
| Diesel engine | 35–45% |
| Natural gas turbine | 35–40% |
| Electric motor | 85–95% |
| Fuel cell | 50–65% |
Worked example: A diesel truck has a 150-liter tank. How far can it travel?
- Total energy: 150 L × 38.6 MJ/L = 5,790 MJ
- Useful energy (40% efficiency): 5,790 × 0.40 = 2,316 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 is wasted as heat — which is why engine cooling systems are so large. Electric vehicles, by contrast, convert over 85% of stored energy into motion.
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.
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