Driving Speed Fuel Calculator
See how much fuel and money a slower motorway speed saves, and how much longer the journey takes.
Your driving
UK unitsWhat slowing down saves
Enter your details to calculate
Fill in the form to see your results.
How this is calculated
- We work out the fuel at your usual speed from your MPG (UK gallons of 4.546 litres).
- Fuel per mile changes with speed using the Department for Transport's figures: 70 mph uses up to 9% more than 60 mph and up to 15% more than 50 mph; 80 mph uses up to 25% more than 70 mph.
- The extra time assumes a steady speed with no hold-ups, so real journeys usually lose less.
Air resistance rises quickly with speed, so most cars use noticeably more fuel per mile above 50-60 mph. The figures are "up to" amounts for a typical car: the saving for yours may be smaller, and a heavy load, roof box or strong headwind makes the difference bigger.
Want to know what the whole trip costs? Try the journey cost calculator, or find cheaper fuel along the way with the route planner.
Use this before a long motorway drive, or to see what easing off on your regular fast-road miles could save over a year.
Common questions
The Department for Transport says driving at 70 mph uses up to 9% more fuel than at 60 mph, and up to 15% more than at 50 mph. At 80 mph a car can use up to 25% more than at 70 mph. The exact figure depends on your car, the load and the weather.
It saves fuel and money but takes longer: 100 miles at 60 mph takes about 14 minutes more than at 70 mph. The calculator shows both, so you can decide whether the saving is worth the extra time.
The MPG you usually get at your normal motorway speed. We work out the MPG at the slower speed from it. If you leave it blank we use our typical-car figure, shown with your result.