How to Compare UK Petrol and Diesel Prices Before a Drive

Petrol and diesel prices can vary between forecourts, so the UK average is a useful benchmark, not a quote for the station you plan to use. Compare the same fuel at nearby stations, allow for any detour, then estimate the trip using your car’s real-world fuel economy. Check live prices again before setting off because pump prices can change.

Use the UK average as a benchmark

RAC Fuel Watch publishes average UK petrol and diesel prices. These figures help show the wider market, but they do not tell you what a particular forecourt is charging. A station near home, work or your route may be above or below the average.

Use the average to put local prices in context. For the decision about where to fill up, compare current prices at the specific stations you could realistically visit. Match petrol with petrol or diesel with diesel. If comparing petrol grades, check that both prices are for the grade your vehicle requires. That keeps the comparison useful: a difference between unlike fuels or grades does not show what you would save by choosing one stop over another.

Compare stations you can reach conveniently

Start with a small set of likely options: a station close to home, one near work, and one you could reach along your planned route. Check each station’s current price and opening details using a live station listing or the forecourt’s own information where available. Listings can become outdated, so confirm the price before making a special trip.

Compare the full cost of the stop, not just the price per litre. A cheaper station may require extra miles, take you away from your route or add time in traffic. If you are already passing it, the detour cost may be negligible; if you would drive out of your way, include that distance in your calculation. The relevant saving depends on how much fuel you buy, while the detour’s cost depends on the extra driving and your car’s consumption.

A simple check is to multiply the price difference per litre by the number of litres you expect to buy. A 3p-per-litre difference saves £1.50 on a 50-litre fill. If reaching the cheaper station adds enough driving to use more than £1.50 of fuel, the detour may erase the saving. This is an estimate: traffic, route and your car’s consumption affect the result. If you only need a small top-up, the same per-litre difference produces a smaller total saving.

Estimate fuel cost for the journey

Use your car’s observed fuel economy rather than assuming an official test figure will match everyday driving. If your dashboard or trip records show miles per gallon (mpg), estimate litres needed with this formula:

Journey litres = miles driven ÷ mpg × 4.546

Then multiply the litres by the price per litre:

Estimated fuel cost = journey litres × price per litre

For example, a 180-mile journey at 40 mpg uses about 20.5 litres (180 ÷ 40 × 4.546). At £1.50 per litre, that is roughly £30.75. The estimate assumes the same average economy for the whole trip; actual use can differ with speed, traffic, weather, load and driving conditions. Add the return distance if you want a round-trip estimate, and use the price for the fuel you expect to buy.

If your car displays mpg for recent trips, use a figure from similar driving where possible. Motorway, town and mixed journeys can produce different results. If you track consumption in litres per 100 km instead, keep distance and units consistent, or use a calculator that accepts those units rather than mixing them with the mpg formula.

Check prices again before setting off

Close to departure, check the route and prices, then compare two or three practical stops. Confirm that each listing is for the right fuel, consider any extra distance and use your own typical economy to estimate the journey cost. If you plan to refuel en route, check the station again before setting off and verify the pump price when you arrive.

The RAC average helps show whether local prices look high or low against the national picture. A current station-specific check is what helps estimate what you may actually pay, while your vehicle’s real-world economy and route determine how much fuel the drive is likely to use.

Source: RAC