UK fuel prices: how each 1p changes your tank and commute

By GlobeBids Money Desk | 1 September 2026

A 1p-per-litre movement in the pump price changes the cost of a 45-litre fill by 45p. A 5p movement changes it by £2.25. Whether that becomes a noticeable monthly saving or increase depends on how much fuel a household buys, not simply the size of the car’s tank.

The Department for Energy Security and Net Zero publishes official weekly UK pump-price statistics. These provide a consistent national reference point, but they are not an unverified same-day price for every forecourt.

What a fuel-price movement does to a 45-litre fill

The calculation is straightforward: multiply the litres bought by the price movement in pounds.

For a 45-litre purchase, a 1p movement means:

45 litres × £0.01 = £0.45

The same arithmetic works for either petrol or diesel. If the price rises, that amount is added to the bill; if it falls, it is the amount saved.

Tank capacity and the amount purchased are not always the same. A driver adding 25 litres after a 3p-per-litre rise would pay 75p more, calculated as 25 × £0.03. Filling a nominally 45-litre tank from half-full would not produce the full 45-litre effect.

How to calculate the effect on a regular commute

Mileage and fuel economy determine how many litres a commute consumes. UK fuel economy is commonly expressed in miles per imperial gallon, with one imperial gallon equal to approximately 4.546 litres.

Use these steps:

• Monthly miles = round-trip commute × commuting days per month.
• Monthly litres = monthly miles ÷ miles per gallon × 4.546.
• Cost of the price movement = monthly litres × movement in pence ÷ 100.

Consider a driver making a 20-mile round trip, five days a week, for four weeks. That is 400 commuting miles. At 40mpg, the commute consumes about 45.46 litres:

400 ÷ 40 × 4.546 = 45.46 litres

A 1p-per-litre movement would therefore alter that month’s commuting fuel cost by about 45p. A 5p movement would change it by approximately £2.27. This example covers commuting only; shopping, school runs and leisure journeys would increase the household total.

A household covering 800 miles under otherwise identical conditions would see roughly twice the effect. A more efficient vehicle would use fewer litres for the same distance, reducing its exposure to each price movement.

Adapt the formula to your own household budget

For a single purchase, use:

Litres bought × price movement in pence ÷ 100 = change in pounds

For monthly driving, use:

Monthly miles ÷ mpg × 4.546 × price movement in pence ÷ 100

To estimate the complete monthly fuel bill rather than only the change, multiply the calculated monthly litres by the actual pump price in pounds per litre. Using the displayed local price produces a more personal estimate than applying a national average.

Why your local forecourt price may be different

An official weekly national figure combines observations into a broad UK measure. A forecourt display represents one location, retailer, fuel grade and moment. Prices can also differ between regions, urban and rural sites, motorway services and competing stations within the same town.

Timing matters too. A weekly average may include prices collected before a particular forecourt changes its board. It is useful for tracking the wider direction and scale of movements, but it does not prove that every driver will encounter the same price or the same weekly change.

Check the journey cost before chasing cheaper fuel

A lower pump price does not automatically make a special trip worthwhile. Compare the potential saving with the fuel consumed on the detour, along with any extra time or parking costs.

Potential saving is calculated as litres purchased × price difference. The detour’s fuel use is calculated as extra miles ÷ mpg × 4.546. Multiply those litres by the local pump price to find the journey cost. A cheaper station already on the route may deliver a genuine saving; a lengthy dedicated drive can absorb it.

Source: Department for Energy Security and Net Zero