Fuel Efficiency (Mass) Converter — MJ/kg, BTU/lb, kWh/kg
Convert between 6 units of fuel energy density — MJ/kg, kJ/kg, kWh/kg, BTU/lb, kcal/kg, and cal/g. Hydrogen at 142 MJ/kg has the highest mass-specific energy of any fuel. Aviation jet fuel (Jet-A) stores ~43 MJ/kg. Lithium-ion batteries store only ~0.7 MJ/kg — 60× less than petrol by mass. Critical for aviation, rocketry and comparing alternative fuels.
Quick conversions
All units
About the Fuel Efficiency (Mass) Converter
Fuel efficiency per unit mass — expressed in MJ/kg, BTU/lb, or kcal/kg — measures the energy content of a fuel relative to its mass. This is also called the specific energy or calorific value and is crucial for comparing fuels in weight-critical applications such as aviation, rocketry, and portable power generation. Hydrogen has the highest mass-specific energy of any fuel at 142 MJ/kg.
Quick facts
- ›Hydrogen fuel: ~142 MJ/kg — the highest mass-specific energy of any chemical fuel
- ›Aviation jet fuel (Jet-A): ~43 MJ/kg — dense energy makes it ideal for long-haul flights
- ›Lithium-ion batteries: only ~0.7 MJ/kg — about 60× less than petrol by mass
- ›Dry wood: ~15 MJ/kg — less than half the energy density of coal (~30 MJ/kg)
Common uses: Aviation, rocketry, automotive engineering, power generation, energy policy