Calculate total energy from a fuel or material by volume or mass, using predefined or custom energy density, with results in MJ, kWh, kJ, and BTU.
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Energy Density Formula
The calculator multiplies the amount of fuel or material by its energy density. Two modes are available depending on whether you measure that amount by volume or by mass.
Per volume:
E = V × ρ_E
Per mass:
E = m × e
- E — total energy released, in MJ
- V — volume of fuel, in L
- ρ_E — volumetric energy density, in MJ/L
- m — mass of fuel, in kg
- e — specific energy (gravimetric energy density), in MJ/kg
Values used are lower heating values (LHV) at standard conditions. LHV assumes water in the combustion products stays as vapor, which matches most engine and turbine applications. For boilers and condensing systems that recover the heat of vaporization, higher heating values (HHV) run roughly 5 to 10 percent above LHV for hydrocarbons. Battery figures are nominal pack-level values and vary with chemistry and design.
Reference Values
Volumetric energy density tells you how much energy fits in a tank. Specific energy tells you how much energy you carry per unit weight. Liquid fuels win on volume; hydrogen wins on mass.
| Fuel | MJ/L | MJ/kg | kWh/kg |
|---|---|---|---|
| Diesel | 38.6 | 45.5 | 12.6 |
| Gasoline | 34.2 | 46.4 | 12.9 |
| Jet fuel / kerosene | 35.0 | 43.0 | 11.9 |
| Propane (liquid) | 25.3 | 46.4 | 12.9 |
| Ethanol | 21.1 | 26.8 | 7.4 |
| LNG | 22.2 | 55.5 | 15.4 |
| Liquid hydrogen | 8.5 | 142.0 | 39.4 |
| Coal (bituminous) | — | 24.0 | 6.7 |
| Wood (dry) | — | 16.0 | 4.4 |
| Li-ion battery pack | 2.6 | 0.875 | 0.24 |
Unit conversions you will run into:
| From | To | Multiply by |
|---|---|---|
| MJ | kWh | 0.2778 |
| MJ | BTU | 947.8 |
| kWh | MJ | 3.6 |
| BTU/lb | MJ/kg | 0.002326 |
| kcal/kg | MJ/kg | 0.004184 |
Worked Example
How much energy is in a 50 L tank of gasoline?
Gasoline has a volumetric energy density of 34.2 MJ/L.
E = 50 L × 34.2 MJ/L = 1,710 MJ ≈ 475 kWh.
That same 50 L weighs about 37 kg, giving 37 × 46.4 = 1,717 MJ. The two methods agree within rounding.
FAQ
Why is liquid hydrogen so weak per liter but so strong per kilogram? Hydrogen has the highest specific energy of any common fuel, but its liquid density is only about 71 kg/m³. You need a large, insulated tank to store a useful amount.
Does this account for engine efficiency? No. The result is the chemical or stored energy in the fuel. A gasoline engine converts roughly 25 to 35 percent of that to useful work. Multiply the result by your efficiency to get shaft or electrical output.
LHV or HHV? The built-in values are LHV. If you need HHV for boiler or fuel-cell calculations, enter a custom density.
Can I use this for natural gas at pipeline pressure? Use the per-mass mode with methane (55.5 MJ/kg), or enter a custom MJ/m³ value matching your pressure and temperature. The built-in LNG figure is for the cryogenic liquid.
