UK Road Trip Fuel Planner: How Much Will It Cost?

A road trip is more fun when you know what it will cost. Estimating the fuel is easy once you have three numbers: the distance, your car's mpg and the price per litre. Here is how.

The formula

Litres needed = miles ÷ mpg × 4.546

Cost = litres × price per litre

The 4.546 converts UK gallons to litres. Use the price in pounds (for example, £1.6956 for 169.56p).

Worked example: 400 miles return

Using the average prices in our database on 6 November 2026: petrol 169.56p and diesel 197.71p a litre.

Your own prices will differ, so check prices near you before you go. For the sums behind the figures, see how to work out your real mpg and cost per mile.

Add a margin

Real-world fuel use is usually higher than your usual figure on a trip, because of luggage, passengers, motorway speeds, roof boxes and winter weather. Add 10 to 20% to be safe. See roof boxes, air con and weight and speed and fuel economy.

Plan your fuel stops

1. Know your range. Tank litres × mpg ÷ 4.546 gives miles. Real-world range is lower, so plan to stop when the tank is about a quarter full.
2. Fill before the motorway. Motorway services charge about 20p a litre more than ordinary stations in our data. See how much more motorway fuel costs.
3. Look for cheaper stations near junctions on your route. Supermarkets are often cheaper. See are supermarket petrol stations cheaper?
4. Check the stop is worth it. Use our break-even sum if it means a detour.

Split the cost

Share the fuel between passengers. A 400-mile petrol trip costing about £77 is under £20 each for four. Agree the method before you go.

Beyond fuel

Add tolls, parking, food and any charges for clean air zones. See hidden motoring costs.

Save fuel on the way

• Drive smoothly and keep to the speed limit.
• Check tyre pressures before you leave. See tyre pressure and fuel economy.
• Remove roof boxes and unneeded weight.
• Use cruise control on steady roads. See cruise control, gears and coasting.
• Plan the route to avoid congestion. See plan your journey to save fuel.

Before you go

Do a quick check of the car. See 10-minute car checks anyone can do. And if you are going far in winter, use our winter car checklist.

Prices are from our database on 6 November 2026 and change daily.