UK petrol and diesel: is a cheaper pump worth the detour?

A pump that is 3p per litre cheaper saves £1.50 on a 50-litre fill. Before an October journey, the useful question is whether reaching that forecourt costs more than £1.50 in extra fuel. Compare the price for the fuel your car uses, estimate how much you will buy, and count only the distance added to your route.

By AtheneNet editors | 30 September 2026

Compare the cost of the fill, not just the price board

Check nearby forecourts for the same fuel grade: petrol against petrol, or diesel against diesel. Multiply the difference in pence per litre by the litres you expect to buy, then divide by 100 to get the saving in pounds. A 3p difference on 20 litres is 60p; on 50 litres it is £1.50.

Use a realistic fill amount. The tank’s full capacity may be much larger than the fuel you need today. Also check that a displayed price applies to your chosen grade and is still available when you arrive. RAC Fuel Watch tracks UK petrol and diesel prices and can provide national context, but a UK-wide figure cannot tell you which nearby pump is cheapest for your journey.

Subtract the fuel used on a detour

Count the extra distance required to visit the cheaper station, including the return to your intended route. Estimate the fuel used with: extra kilometres × your car’s litres per 100 km ÷ 100. Multiply that result by the pump price in pounds per litre. A forecourt already on your route may add little or no driving distance.

A 50-litre fill: £1.50 saved at the pump, about 62p overall

Suppose one station charges 150p per litre and another charges 147p. These are illustrative prices, not current UK averages or quoted forecourt prices. Buying 50 litres at the cheaper pump saves £1.50.

Now suppose reaching it adds 10 km and your car uses 6 litres per 100 km. The detour uses about 0.6 litres, costing roughly 88p at 147p per litre. The estimated saving falls to about 62p. Traffic, idling and your actual fuel consumption can change that result; time spent on the detour also matters even though it is not included in the fuel calculation.

Before setting off, check the current local prices and opening hours. If the cheaper station fits naturally into your October route, recalculate using only the distance it actually adds.

Source: RAC