Fuel Efficiency (Mass) Converter
ScienceConvert mass-based fuel efficiency between km/kg, miles/kg, and kg/100km — used for hydrogen and CNG/LNG vehicles measured by fuel mass, not volume.
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What is a Fuel Efficiency (Mass)?
The Fuel Efficiency (Mass) Converter converts fuel efficiency measured by fuel mass rather than fuel volume — kilometres per kilogram, miles per kilogram, and kilograms per 100 kilometres. This distinction matters for hydrogen fuel cell and CNG/LNG vehicles, which are fuelled and metered by weight rather than the litres or gallons used for gasoline and diesel.
Because km/kg (and mi/kg) measure distance per unit fuel while kg/100km measures fuel per unit distance, converting between them is a reciprocal relationship, not a simple multiplication — the same pattern as the existing Fuel Efficiency Converter uses for volume-based L/100km versus km/L.
How to use this Fuel Efficiency (Mass) calculator
- Choose your starting unit from the source dropdown — for example, "Kilometres per Kilogram (km/kg)".
- Enter the numeric value you want to convert in the input field.
- Choose your target unit from the destination dropdown — for example, "Kilograms per 100 km (kg/100km)".
- Read the converted result, which updates instantly as you type or change units.
- Use the swap (⇅) button if you need to reverse the conversion direction.
- Use the copy button to grab the result for a vehicle comparison or fleet efficiency report.
Formula & Methodology
The converter's canonical unit is km/kg. Conversions follow: - mi/kg → km/kg: multiply by 1.609344 (exact) - kg/100km ↔ km/kg: reciprocal relationship — km/kg = 100 ÷ kg/100km, and kg/100km = 100 ÷ km/kg Worked example — converting 100 km/kg (a typical hydrogen fuel cell vehicle) to kg/100km: kg/100km = 100 ÷ 100 = 1.0 kg/100km This means the vehicle consumes about 1 kilogram of hydrogen for every 100 kilometres travelled — a useful reference figure for comparing against other hydrogen vehicles or fuel cost calculations. For background on the underlying term, see our glossary entry on Fuel Efficiency.
Frequently Asked Questions
Hydrogen, CNG (compressed natural gas), and LNG (liquefied natural gas) vehicles typically fuel by mass (kilograms) rather than volume (litres or gallons), since gaseous fuels are compressed to varying densities and mass is the more consistent, meaningful measurement for how much fuel was actually delivered.
Divide 100 by the km/kg value, since these two units are reciprocals of each other — a higher km/kg value (more distance per kilogram) corresponds to a lower kg/100km value (less fuel needed per 100 km), and vice versa.
km/kg measures distance per unit of fuel mass, while kg/100km measures fuel mass per unit of distance — these are inverse relationships, not proportional ones, so converting between them requires division (100 ÷ value) rather than multiplication by a fixed factor, the same pattern as L/100km versus km/L for liquid fuel.
The [Fuel Efficiency Converter](/fuel-efficiency-converter/) covers volume-based fuel efficiency (km/L, L/100km, MPG) for liquid fuels like gasoline and diesel, while this converter covers mass-based fuel efficiency (km/kg, kg/100km) for gaseous fuels like hydrogen and CNG, which are dispensed and measured by weight rather than volume.
Hydrogen fuel cell vehicles commonly achieve roughly 90 to 120 km per kilogram of hydrogen, though this varies by vehicle model and driving conditions — use this converter to compare that figure against a kg/100km or mi/kg equivalent from a different source.
Multiply the mi/kg value by 1.609344, since one mile equals 1.609344 kilometres. Enter your value with 'Miles per Kilogram (mi/kg)' as the source and 'Kilometres per Kilogram (km/kg)' as the target to apply this automatically.
Not directly, since they use different fuel measurement bases (mass for hydrogen, volume for gasoline) with very different energy content per unit — a fair comparison requires converting both to an energy-equivalent basis (like cost or energy per 100 km) rather than comparing km/kg against MPG directly.
Using a fixed 100 km reference distance (rather than expressing efficiency as a per-kilometre rate) keeps the numbers in a convenient, easily comparable range, mirroring the same convention used for L/100km in liquid-fuel efficiency reporting in most of the world outside the US.
Yes — any application where fuel is measured and dispensed by weight rather than volume, including some industrial and aviation contexts, can use mass-based efficiency metrics, though hydrogen and natural gas vehicles are the most common consumer-facing example.
The 1.609344 km-per-mile conversion factor is exact by international agreement, so converting mi/kg to km/kg introduces no rounding error beyond the precision of your original figure.
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