Working out diesel costs
The calculation is the same as for petrol: litres needed = (miles ÷ MPG) × 4.546, then multiply by the diesel price. What differs is the typical inputs — diesel tends to be a few pence dearer per litre, while many diesel cars return higher MPG.
Example: a 250-mile motorway trip
An estate car averaging 55 MPG on the motorway uses about 20.7 litres for 250 miles. At £1.52 a litre that's roughly £31.41.
Towing and heavy loads
If you tow a caravan or trailer, expect your MPG to drop noticeably. Enter a lower MPG to reflect this — your trip computer's reading from a previous tow is the best guide.
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.
For a quick per-mile figure, try the diesel cost per mile calculator.