Convert between m/kg, km/kg, mi/lb and more fuel efficiency by mass units.
Fuel efficiency by mass measures how far a vehicle travels per unit mass of fuel consumed. This is relevant for aviation and rocketry where fuel weight matters more than volume.
Fuel Efficiency Converter • Fuel Efficiency - Volume Converter
Standard fuel economy (mpg, L/100km) measures distance per volume. Fuel efficiency by mass measures distance per kg of fuel. This is more physically meaningful because fuel energy is proportional to mass (specific energy). Hydrogen fuel cells use kg as the fuel unit. Comparing fuels by mass: 1 kg petrol = 43.2 MJ; 1 kg diesel = 45.6 MJ; 1 kg hydrogen = 142 MJ — hydrogen is 3× more energy-dense by mass than petrol.
| Fuel | MJ per kg | Use |
|---|---|---|
| Petrol (gasoline) | 43.2 | Passenger cars |
| Diesel | 45.6 | Trucks, long-distance |
| Jet A-1 | 43.2 | Commercial aviation |
| Hydrogen | 142.0 | Fuel cells, rockets |
Fuel economy by mass is most relevant in aviation and maritime shipping, where fuel is loaded and tracked by weight (kg or tonnes) rather than volume. Aircraft fuel tanks are measured in kilograms because fuel density changes with temperature; a 1 °C rise decreases Jet A-1 density by about 0.0007 g/mL. Airlines use kg to ensure accurate load calculations regardless of ambient temperature. Ships measure bunker fuel in metric tonnes (1,000 kg). For consumer vehicles, mass-based efficiency is rarely used because volume is more practical at the pump.
Fuel efficiency per unit mass measures how far a vehicle travels per unit of fuel mass rather than volume. Common units include miles per pound (mi/lb), kilometres per kilogram (km/kg), and metres per gram (m/g). This is particularly useful for aircraft and rockets where mass matters more than volume (fuel density varies with temperature and fuel type), and for comparing jet fuel (kerosene), petrol, diesel, and hydrogen on a common mass basis.
Aviation uses specific fuel consumption (SFC) in lb/hr/lbf or g/(kN·s) to measure engine efficiency. Hydrogen fuel cells are compared on a mass basis because hydrogen's energy density by mass (120 MJ/kg) is three times that of petrol (44 MJ/kg), even though it has very low volumetric density. This converter helps compare these metrics across propulsion technologies.
| Fuel | MJ/kg | MJ/L | Notes |
|---|---|---|---|
| Hydrogen | 120 | 8.5 (700 bar) | Highest by mass |
| Petrol (gasoline) | 44 | 32 | Most common fuel |
| Diesel | 45 | 38 | Higher than petrol |
| Jet fuel (Jet-A) | 43 | 34 | Aviation standard |
| Battery (Li-ion) | 0.7 | 1.5 | Electric vehicles |
Mass-based fuel efficiency (distance per unit of mass) is the preferred measure in aviation and heavy industry because fuel volume changes with temperature while mass remains constant. Jet aircraft fuel efficiency is commonly expressed in nautical miles per kilogram or miles per pound. Freight and shipping efficiency uses tonne-kilometers per liter of fuel as a combined productivity metric. In these contexts, a full mass-to-volume conversion also requires knowing fuel density: Jet-A aviation fuel has a density of approximately 0.800 kg/L at standard conditions, but this varies from 0.775 to 0.840 kg/L depending on temperature. Ship fuel (bunker oil) varies significantly in density between grades. Rail freight efficiency is often quoted in ton-miles per gallon or gram of CO&sub2; per ton-kilometer. Mass-based efficiency figures are particularly valuable when comparing aircraft at different fueling temperatures or when regulatory reporting requires mass-normalized emissions data rather than volume-normalized consumption figures.
| Mass unit | Liters equivalent (Jet-A) | Context |
|---|---|---|
| 1 kg Jet-A | 1.25 L | Commercial aviation |
| 1 lb Jet-A | 0.567 L | US general aviation |
| 1 tonne bunker oil | ~1050 L | Maritime shipping |
