How to calculate fuel consumption
- 1.
Choose a unit system
Select metric, US or UK units to match your odometer and fuel measure.
- 2.
Enter fuel and distance
For a real-world measurement, enter the fuel used and distance driven between fill-ups.
- 3.
Add a fuel price
Optionally enter the price per litre or gallon to see estimated running costs.
- 4.
Review the results
Compare the equivalent economy figures or switch to trip mode to estimate fuel required.
Fuel economy formula and a worked example
In metric units, fuel consumption is commonly expressed as litres per 100 kilometres. Divide the litres used by the kilometres driven, then multiply by 100:
L/100 km = litres used ÷ kilometres driven × 100
For example, if a car uses 42 litres over 650 km, its consumption is 42 ÷ 650 × 100 = 6.46 L/100 km. Lower L/100 km means better efficiency. To estimate fuel for a journey, reverse the calculation: litres needed = distance × L/100 km ÷ 100. A 350 km trip at 6.5 L/100 km needs about 22.75 litres. Add a fuel price to estimate the cost, but remember that traffic, route and weather can change the actual result.
Convert L/100 km, km/L and miles per gallon
MPG means miles per gallon. Unlike L/100 km, a higher MPG figure indicates better fuel economy. The US and UK gallons have different volumes, so their MPG figures are not interchangeable: one US gallon is about 3.785 litres and one imperial (UK) gallon is about 4.546 litres.
- km/L = 100 ÷ L/100 km
- US MPG = 235.215 ÷ L/100 km
- UK MPG = 282.481 ÷ L/100 km
For instance, 6 L/100 km is about 16.7 km/L, 39.2 US MPG or 47.1 UK MPG. This tool converts between all four values so you can compare a vehicle specification, a rental-car listing or your own driving log. Select the matching system when planning a trip so distance and fuel units stay consistent.
Measure your real-world fuel economy
A dashboard display is useful for quick comparisons, but it may differ from fuel actually used. For a more reliable measurement, fill the tank to the same point, reset the trip odometer, drive normally, then refill and record the litres added and distance travelled. The second fill amount approximates the fuel used over that distance. Repeat for several tanks and calculate the combined average to reduce variation from pump shut-off and small fill differences.
Fuel economy changes with speed, stop-and-go traffic, temperature, hills, tyre pressure, vehicle load and air conditioning. A short city trip is not directly comparable with a long motorway journey. Compare similar routes and seasons when tracking a change. Smooth acceleration, sensible motorway speeds, correctly inflated tyres and removing unused roof racks can help reduce consumption. Treat every calculator result as an estimate based on the figures you enter.
Frequently asked questions
How do I calculate fuel consumption per 100 km?
+
Divide the litres used by the kilometres driven and multiply by 100. Using 30 litres over 500 km gives 30 ÷ 500 × 100 = 6 L/100 km.
How do I convert L/100 km to MPG?
+
Divide 235.215 by L/100 km for US MPG, or 282.481 for UK MPG. At 6 L/100 km, that is about 39.2 US MPG or 47.1 UK MPG.
What is the difference between US and UK MPG?
+
A US gallon is smaller than an imperial gallon, so the same vehicle has a higher numerical UK MPG figure. Choose the correct gallon standard when comparing ratings.
How much fuel will I need for a trip?
+
Multiply distance in kilometres by L/100 km and divide by 100. A 500 km trip at 7 L/100 km uses about 35 litres.
How can I measure my car’s actual fuel economy?
+
Fill up, record or reset the trip distance, then refill and record the litres added. Use the distance and fuel amount in the calculator. Several fill-ups give a steadier average.
Does a higher MPG mean better fuel economy?
+
Yes. MPG measures miles travelled per gallon, so a higher figure means more distance from the same amount of fuel. For L/100 km, lower is better.
Updated: