How petrol journey costs are worked out
Petrol is sold by the litre, but UK cars are rated in miles per imperial gallon. The calculator converts your MPG into litres per mile (4.546 ÷ MPG), multiplies by the distance, then by the petrol price.
Example: a 120-mile round trip
A petrol hatchback averaging 45 MPG uses about 12.1 litres over 120 miles. At £1.45 a litre that's around £17.58. The same trip in a petrol SUV doing 32 MPG would cost about £24.72.
Unleaded vs super unleaded
Most petrol cars in the UK run happily on standard E10 unleaded. Super unleaded (E5) costs more per litre and, for most everyday cars, doesn't save enough fuel to cover the difference. Some performance cars and older vehicles need E5 — check your handbook.
Petrol vs diesel fuel costs
Diesel usually costs a little more per litre than petrol, but diesel cars typically achieve better fuel economy, especially on longer motorway runs. Whether diesel works out cheaper per mile depends on the specific cars being compared, the prices you pay and how you drive.
Neither fuel is always cheaper. The fairest comparison is cost per mile: use the petrol cost per mile and diesel cost per mile calculators with your own figures.
How can I reduce my fuel costs?
Small habits add up over a year of driving. None of these are dramatic on their own, but together they can noticeably improve your real-world MPG:
- Accelerate and brake smoothly. Reading the road ahead and avoiding harsh acceleration uses less fuel.
- Keep tyres at the correct pressure. Under-inflated tyres increase rolling resistance. Check the pressures in your handbook or on the door pillar.
- Remove unnecessary weight. Clear out the boot and take off empty roof boxes and bars when you don't need them.
- Plan journeys and combine trips. A warm engine is more efficient, so one longer round trip often beats several short ones.
- Keep the car maintained. Regular servicing keeps the engine running as intended.
- Compare fuel prices. Prices can vary between nearby forecourts, and motorway services are often more expensive.
Want a quick per-mile figure instead? Use the petrol cost per mile calculator.