UK petrol and diesel rise: what a 50-litre fill costs

A 50-litre fill-up at the latest UK average price costs about £86.01 for petrol or £97.77 for diesel. Both national averages rose in the week commencing 21 September 2026. That matters to drivers budgeting for their next stop, but the price on a nearby pump may be different. Check the displayed price before filling and use it to calculate your own likely bill.

The Department for Energy Security and Net Zero puts petrol at 172.01p per litre, up from 168.14p the preceding week. Diesel averages 195.53p per litre, up from 190.72p. The figures appear in the government’s weekly road fuel prices, published on 22 September.

Petrol rose 3.87p and diesel 4.81p per litre in a week

The government’s weekly data gives the following national averages. Each price is in pence per litre; the dates are the weeks commencing 14 and 21 September 2026.

For an illustrative 50 litres, the change in the average price adds roughly £1.94 to a petrol fill and £2.41 to a diesel fill compared with the preceding week’s averages. Those are comparisons for the same volume of fuel. A driver buying fewer litres will see a smaller difference in pounds; one buying more will see a larger one.

Diesel’s latest national average is 23.52p per litre above petrol’s. At 50 litres, that works out to £11.76 more. It compares the cost of the same volume at the two averages, rather than the cost of driving the same distance: vehicles can use different amounts of fuel for a journey.

These two weekly readings establish that the national averages rose between the stated weeks. They do not, by themselves, show how long the increase will last or where prices will go next. For a household budget, the immediate takeaway is the cost of the litres you expect to buy at the price available to you.

Your local pump price may differ from the UK average

A national average summarises prices across the UK. It is a useful benchmark for seeing the broad weekly change, but it is not a quote from any particular forecourt. The price you pay is the one displayed for your fuel at the station where you fill up. It may sit above or below the reported average.

That distinction matters when planning a trip or comparing nearby stations. The £86.01 petrol and £97.77 diesel examples use the latest national figures and an assumed 50-litre purchase. Neither figure is a guaranteed receipt total. Your bill depends on both the pump price and how many litres you actually put in the tank.

Calculate your own fill-up cost from the pump price

Multiply the displayed price in pence per litre by the number of litres you plan to buy, then divide by 100 to get pounds. For example, at the national petrol average, 172.01 × 50 ÷ 100 = £86.005, or about £86.01 when expressed to the nearest penny. At the diesel average, 195.53 × 50 ÷ 100 = £97.765, or about £97.77.

You can use the same calculation before buying fuel: substitute the price shown at your chosen pump and your expected number of litres. If you usually buy a set amount of fuel rather than fill the tank, use that amount instead of 50 litres. For the closest estimate on the day, check the forecourt price immediately before you fill up.

Source: UK government