Fuel Consumption Calculator
Enter the distance you drove and the fuel you used to get your fuel economy in every common unit: miles per gallon (US and UK), kilometres per litre, and litres per 100 kilometres. Add a fuel price to see your trip cost per mile or kilometre, and check the estimated CO2 emitted. Switch between metric and imperial units at any time.
How fuel consumption is measured
Fuel consumption is the amount of fuel a vehicle uses to travel a given distance. It is expressed in two equivalent ways: as fuel per distance (litres per 100 kilometres, L/100 km) or as distance per fuel unit (miles per gallon, km/L). Both measure the same thing from opposite directions, so you can convert between them by dividing a constant by the other value. Specifically, L/100 km = 235.215 / MPG (US) and MPG (US) = 235.215 / L/100 km. Lower L/100 km means better efficiency; higher MPG means better efficiency. European and most Asian markets use L/100 km, while the United States and older UK vehicles use MPG.
How to measure your real-world fuel consumption
The most accurate method is the brim-to-brim fill-up test. Fill your tank to the brim, reset your trip odometer to zero, drive your normal mix of roads, then return to the same pump and fill to the brim again. The litres shown on the pump and the kilometres on the odometer are your inputs. Divide fuel by distance and multiply by 100 for L/100 km, or divide distance by fuel for km/L. Repeat for two or three tanks to average out variation from traffic, load and weather. Your on-board trip computer typically reads 5 to 15 percent better than the real fill-up figure, because manufacturers calculate it using instant injection data rather than a calibrated pump.
What affects fuel consumption?
Driving speed has the largest single effect: aerodynamic drag rises with the square of velocity, so motorway driving above 100 km/h (62 mph) burns substantially more fuel per kilometre than urban speeds of 50-60 km/h. Tyre pressure below specification can add 1-3 percent to fuel use. Air conditioning on hot days adds 5-15 percent in city conditions. Carrying extra load (roof boxes, cargo) and cold engine warm-up periods both raise consumption. Smooth acceleration and anticipatory braking can cut fuel use by 10-15 percent compared to aggressive driving. A clogged air filter or old spark plugs reduce combustion efficiency and are cheap fixes that improve economy immediately.
CO2 emissions and fuel economy
Burning one litre of petrol (gasoline) releases approximately 2,310 grams of carbon dioxide, regardless of which vehicle burns it - the CO2 comes from the carbon in the fuel, not the engine. Diesel releases slightly more CO2 per litre (approximately 2,640 g/L) but typically delivers better km/L, so net CO2 per kilometre is similar or lower. The CO2 estimate in this calculator uses the petrol figure. To compare vehicles meaningfully, use grams of CO2 per kilometre (g/km), which is the standard used by the European Union and UK for vehicle taxes and labelling. A typical new European car emits around 120-160 g/km; hybrids are typically 70-110 g/km; battery electric vehicles emit zero at the tailpipe.
Typical fuel consumption by vehicle type
| Vehicle type | L/100 km | MPG (US) | MPG (UK) | Efficiency |
|---|---|---|---|---|
| Hybrid car | 4.0 - 5.5 | 43 - 59 | 51 - 71 | Excellent |
| Small city car | 5.0 - 6.5 | 36 - 47 | 43 - 56 | Very good |
| Compact sedan | 6.0 - 8.0 | 29 - 39 | 35 - 47 | Good |
| Mid-size sedan | 7.5 - 9.5 | 25 - 31 | 30 - 37 | Average |
| SUV / crossover | 9.0 - 12.0 | 20 - 26 | 24 - 31 | Below average |
| Large SUV / truck | 12.0 - 18.0 | 13 - 20 | 16 - 24 | Poor |
| Performance car | 10.0 - 20.0 | 12 - 24 | 14 - 28 | Poor |
Approximate real-world L/100 km and MPG (US) for common vehicle categories. Actual figures vary by model, load and driving conditions.
Frequently asked questions
How do I calculate fuel consumption in L/100 km?
Divide the litres of fuel used by the distance driven in kilometres, then multiply by 100. For example, if you used 8 litres to drive 100 km, your consumption is (8 / 100) x 100 = 8 L/100 km. If you drove 250 km and used 18 litres, the answer is (18 / 250) x 100 = 7.2 L/100 km.
How do I convert L/100 km to MPG?
To convert L/100 km to US MPG, divide 235.215 by the L/100 km figure. For UK MPG, divide 282.481. So 8 L/100 km equals 235.215 / 8 = 29.4 MPG (US) or 282.481 / 8 = 35.3 MPG (UK). The reverse works the same way: US MPG to L/100 km is 235.215 / MPG.
What is the difference between US gallons and UK gallons?
A US gallon is 3.785 litres, while a UK (imperial) gallon is 4.546 litres - about 20 percent larger. This means that UK MPG figures are always about 20 percent higher than US MPG for the same vehicle. A car that gets 30 MPG (US) gets approximately 36 MPG (UK). Always check which gallon a manufacturer or publication is using.
Why is my on-board computer more optimistic than the fill-up calculation?
On-board fuel computers calculate consumption from fuel injector pulse data, which is not as accurate as measuring actual litres dispensed by a calibrated pump. They also sometimes exclude fuel used during cold starts and idling before the engine management system is active. The fill-up method is the most accurate and is the standard used in official tests.
How much does tyre pressure affect fuel consumption?
Under-inflated tyres increase rolling resistance, which raises fuel consumption. A typical 20 kPa (3 PSI) under-inflation in all four tyres can add 1-3 percent to fuel use. Keeping tyres inflated to the recommended pressure shown on the door sill sticker is one of the easiest and cheapest ways to maintain good fuel economy.
How do I calculate fuel cost per kilometre?
Multiply your fuel consumption in L/100 km by the price per litre, then divide by 100. For example, at 8 L/100 km and a price of $1.80 per litre, the cost is (8 x 1.80) / 100 = $0.144 per kilometre, or 14.4 cents per km. This calculator works out the per-km and per-mile cost automatically when you enter a fuel price.