Fuel Consumption Calculator — L/100km, MPG & km/L
Measure your vehicle's actual fuel consumption from a fill-to-fill trip: enter the distance driven and the fuel used, and get L/100 km, km/L, US MPG, UK MPG and a CO₂ estimate — all at once in metric and imperial.
Units
km
L
Litres of fuel per 100 kilometres driven
- 1
Fuel per km
40 ÷ 400 = 0.1 - 2
Litres per 100 km
0.1 × 100 = 10
How does this calculator work?
Fuel consumption = fuel used (L) ÷ distance (km) × 100 gives L/100 km. Flip to km/L = distance ÷ fuel. Convert to US MPG ÷ 235.2 or UK MPG ÷ 282.5. Enter your fill-to-fill data to get all four metrics plus a CO₂ estimate for petrol and diesel.
Formula
How this is calculated
The most accurate way to measure real-world fuel consumption is the fill-to-fill method: fill your tank completely, drive a measured distance, refill completely and record exactly how many litres (or gallons) went back in. That fuel quantity divided by the distance gives your consumption.
In metric notation, fuel consumption is expressed as litres per 100 kilometres (L/100 km), where a lower number means a more efficient vehicle — a modern petrol car typically runs at 5–8 L/100 km on a highway, and a hybrid might achieve 3–5 L/100 km. In efficiency notation (km/L or MPG), a higher number is better. US and UK (imperial) miles per gallon differ because the UK gallon is larger: 1 UK gallon = 4.546 L versus 1 US gallon = 3.785 L, so UK MPG is always about 20 % higher than US MPG for the same vehicle.
The CO₂ estimates use standard emission factors: burning one litre of petrol produces approximately 2.31 kg CO₂, and one litre of diesel produces approximately 2.68 kg CO₂ (well-to-wheel figures are higher but vary by region). These are combustion-only estimates from published IPCC and government data (2023) and do not include vehicle manufacturing emissions.
Frequently asked questions
For petrol passenger cars, 5–7 L/100 km (40–47 US MPG) is good; under 5 L/100 km is excellent. Diesel is typically 1–1.5 L/100 km lower for the same vehicle. City driving raises consumption by 20–40 % versus motorway/highway driving due to stop-start traffic.
The US gallon (3.785 L) is smaller than the UK imperial gallon (4.546 L). The same vehicle that returns 30 US MPG achieves about 36 UK MPG — a 20 % difference. Always check which gallon a spec sheet uses before comparing vehicles.
This calculator measures efficiency from actual trip data (distance + fuel consumed). The fuel cost calculator estimates how much a planned trip will cost given an assumed efficiency and fuel price. Use this one after a trip to benchmark real consumption; use the cost calculator to plan a future trip budget.
Also known as
TG we-Calculate Editorial Team. (2026). Fuel Consumption Calculator — L/100km, MPG & km/L [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/fuel-consumption-calculator
TG we-Calculate Editorial Team. "Fuel Consumption Calculator — L/100km, MPG & km/L." TG we-Calculate. 2026. https://we-calculate.com/calculator/fuel-consumption-calculator.
TG we-Calculate Editorial Team, "Fuel Consumption Calculator — L/100km, MPG & km/L," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/fuel-consumption-calculator
@misc{wecalculate_fuel_consumption_calculator, title = {Fuel Consumption Calculator — L/100km, MPG & km/L}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/fuel-consumption-calculator}}, year = {2026}, note = {TG we-Calculate} }
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