What Is Fuel Consumption?
Fuel consumption measures how much fuel your vehicle burns over a given distance. It's the inverse of fuel economy: while fuel economy tells you how far you travel per unit of fuel (e.g., kilometres per litre), fuel consumption expresses how much fuel you need per unit distance (e.g., litres per 100 km).
The two metrics are directly related. A car with high fuel economy has low consumption, and vice versa. Understanding consumption is valuable for budgeting, identifying when a vehicle needs servicing, and comparing the true running costs of different cars. Most European countries prefer litres per 100 km, while the US typically uses miles per gallon (MPG).
Fuel Consumption Formula
Fuel consumption is calculated by dividing the total fuel used by the distance travelled. You can also derive it by taking the reciprocal of fuel economy.
Fuel consumption = Fuel used ÷ Distance travelled
Fuel consumption = 1 ÷ Fuel economy
Trip cost = Fuel used × Price per unit
Fuel used— Total fuel consumed during the journey, measured in litres, gallons, or other volume unitsDistance travelled— Total distance covered, measured in kilometres, miles, or other distance unitsFuel economy— How far the vehicle travels per unit of fuel (e.g., km/L or MPG)Price per unit— Cost of fuel per litre, gallon, or other volume unit
How to Calculate Fuel Consumption
Start with two known values: the distance your vehicle travelled and the amount of fuel it consumed. Divide fuel by distance to get consumption in the original units (e.g., L/km). To convert to standard metrics:
- Litres per 100 km: Divide fuel in litres by distance in kilometres, then multiply by 100.
- Miles per gallon (MPG): Divide distance in miles by fuel in US or imperial gallons.
- Kilometres per litre: Divide distance in kilometres by fuel in litres.
Example: A car uses 60 litres to travel 800 km. Consumption = (60 ÷ 800) × 100 = 7.5 L/100km.
Calculating Trip Fuel Cost
Once you know fuel consumption, multiplying by fuel price reveals your trip's true cost. If your vehicle consumes 8 L/100km and fuel costs €1.50 per litre, a 500 km journey burns 40 litres, costing €60 in fuel alone.
Track this metric regularly to spot rising consumption, which often signals engine problems, underinflated tyres, or excessive idling. Compare consumption across different routes and seasons to understand what factors affect your vehicle's efficiency. Heavier loads, city driving, and cold weather typically increase consumption.
Common Pitfalls and Considerations
Avoid these mistakes when measuring and interpreting fuel consumption data.
- Measuring from empty tank may be inaccurate — Filling to the absolute maximum can trap air in the fuel line. Instead, fill until the pump clicks off once—this gives more consistent measurements across fill-ups and reduces error.
- City vs. highway driving skews results — Urban driving with traffic lights and acceleration burns more fuel than steady motorway cruising at constant speed. Separate your measurements by driving type, or calculate consumption across longer periods to average out variations.
- Vehicle load and weather affect consumption — A roof rack, extra passengers, or towing a trailer significantly increases consumption. Cold weather also worsens efficiency because the engine runs rich initially and tyres lose pressure. Note these variables when comparing results over time.
- Don't rely on dashboard fuel economy readings alone — In-car computers estimate consumption but often overestimate efficiency. Cross-check with manual calculations using pump receipts and odometer readings for accuracy.