Advanced options
What The Fuel Cost Calculator Works Out
- Fuel cost: miles divided by MPG gives gallons, multiplied by 4.546 gives litres (a UK gallon, not the smaller US one), multiplied by the pump price gives the cost. A 100-mile trip at 40mpg and 167p a litre is about GBP 19.
- Fuel used: the litres burned, with the gallon equivalent underneath. A typical tank holds 45 to 60 litres.
- Cost per mile: fuel cost divided by distance. Most petrol and diesel cars sit between 12p and 25p a mile for fuel alone at current prices; large SUVs and vans can be 30p or more.
- Fuel economy entered as (advanced): switch between UK mpg, litres per 100 km (as shown by many European cars and spec sheets) and miles per litre. Everything is converted to mpg behind the scenes: 5.6 L/100km is about 50mpg.
- Real-world adjustment (advanced): trims the figure you entered. Official WLTP figures are typically 10% to 20% better than drivers actually achieve, and motorway speed is the biggest factor: 80mph burns roughly 10% to 15% more than 70mph.
- Cost per person (advanced): the trip cost, including tolls and parking, divided between everyone sharing. Three people sharing a 100-mile return trip usually beats three rail tickets.
- Annual cost of this trip (advanced): the trip cost multiplied by how often you make it. A 20-mile daily commute at 40mpg is roughly GBP 950 a year in fuel alone, more than most drivers guess.
- True cost including wear (advanced): the distance at a full running-cost rate. HMRC's 45p per mile approved rate is a fair estimate of the real cost once tyres, servicing, insurance and depreciation are included, and is the honest figure for splitting costs with passengers or comparing with the train.
- CO2 emitted (advanced): litres multiplied by 2.31 kg for petrol or 2.68 kg for diesel (DEFRA conversion factors). The average UK car emits around 2 tonnes a year.
- Saving at 10% better MPG (advanced): what gentler driving, correct tyre pressures and removing roof boxes would save on this trip. Supermarket forecourts are usually cheapest; motorway services run 15p to 20p a litre dearer.
Source and further reading: RAC Fuel Watch.