UK fuel costs: the real price of a 300-mile journey

A 300-mile journey uses about 38.97 litres in a car averaging 35 miles per imperial gallon, compared with 24.80 litres at 55mpg. The final bill depends on the latest petrol or diesel price, so drivers should insert the current official UK average—or a confirmed local forecourt price—into the calculation below.

By GlobeBids Consumer Desk
Calculation guide: 16 August 2026

Use the latest verified UK pump-price averages

The Department for Energy Security and Net Zero publishes the official weekly road fuel prices, covering average UK pump prices for unleaded petrol and diesel.

No dated numerical observation for August 2026 has been verified for this guide, so an unconfirmed figure is not presented as the latest price. Before calculating, open the official series and note the newest publication date and its petrol or diesel price in pence per litre.

The national average is a benchmark, not a promise of the price at a particular filling station. Motorway services can have different operating costs and competitive conditions, while supermarkets may price fuel as part of a wider retail strategy. Regional supply, property and transport costs can also affect local prices.

The numbers that shape the bill

• A 35mpg car needs approximately 38.97 litres for 300 miles.
• A 55mpg car needs approximately 24.80 litres for the same journey.
• Each 1p-per-litre change alters these example costs by about 39p and 25p respectively.
• Your car’s actual consumption may differ because of traffic, weather, load and driving style.

Calculate a 300-mile fuel bill

UK economy figures normally use miles per imperial gallon. Convert that figure into litres consumed with this formula:

Litres used = miles ÷ mpg × 4.546

Then calculate the bill:

Journey cost = litres used × price per litre

If the published price is in pence, divide it by 100 before multiplying. A petrol price of P pence per litre therefore becomes £(P ÷ 100) per litre.

For a purely illustrative price of £1.40 per litre—not a claimed current UK average—the 35mpg journey would cost £54.55, while the 55mpg journey would cost £34.71. That is a £19.84 difference over 300 miles.

Recalculate with a local price

Suppose the nearest forecourt displays 142.7p per litre. Convert that to £1.427, then multiply it by the litres your car is expected to use. At 35mpg, the calculation would be 38.97 × £1.427, producing an estimated cost of £55.61.

Label each assumption when comparing options: journey distance, fuel type, expected mpg and price per litre. If the route includes congestion, steep roads or extensive motorway driving, consider using the car’s recent real-world mpg rather than its advertised figure.

Reduce the cost without compromising safety

Small preparation steps can lower consumption or prevent an unnecessarily expensive refill:

• Compare confirmed prices at nearby stations before departure, without making a long detour that consumes the saving.
• Check tyre pressures when the tyres are cold and follow the vehicle manufacturer’s specification.
• Remove unnecessary items from the boot or roof rack to reduce weight and aerodynamic drag.
• Accelerate progressively, anticipate traffic and maintain a steady legal speed where conditions permit.
• Never coast in neutral, switch off the engine while moving or reduce tyre pressure to save fuel.

The calculation is an estimate rather than a guarantee. Diversions, idling, heating or air-conditioning use, passenger load and driving conditions can all change consumption. The most useful final check is the dated official UK average alongside the actual price shown at a convenient forecourt on the route.

Source: UK Department for Energy Security and Net Zero