--- title: "Fuel Cost Calculator for UK Drivers: Miles, mpg, Litres | AumnI tools" description: "Price a UK journey in miles from mpg and the pence-per-litre pump price, compare two cars with an electric one, split the cost and see the CO₂ for each." url: https://aumnitools.com/uk/tool/fuel-cost-calculator category: "Lifestyle" country: "United Kingdom" updated: 2026-11-08 --- # Fuel Cost Calculator UK petrol is sold by the litre, but car economy is still quoted in miles per imperial gallon and journeys in miles. This version opens in miles, litres and mpg (UK), fills in the latest weekly average pump price from the Government, and prices the same trip for as many cars as you add, including an electric one. ## United Kingdom rules and figures - UK pumps sell petrol and diesel by the litre, while drivers quote economy in miles per imperial gallon and distances in miles, so this page starts in miles with litres and mpg (UK). - DESNZ published an average unleaded petrol price of 1.7278 pounds per litre for the week of 2 November 2026. Weekly prices move, so type your own pump price over it. - The Vehicle Certification Agency’s official fuel consumption label shows both litres per 100 km and miles per gallon, using the imperial gallon. - Speeds on UK roads are signed in miles per hour, and the currency used in the price boxes is the pound sterling. Sources: [DESNZ: Weekly road fuel prices](https://www.gov.uk/government/statistics/weekly-road-fuel-prices) (checked 2026-11-08); [Vehicle Certification Agency: Fuel consumption labelling](https://www.vehicle-certification-agency.gov.uk/fuel-consumption-co2/fuel-consumption-labelling/) (checked 2026-11-08) ## How the fuel cost calculator works Each mpg (UK) figure is turned into litres per 100 km, because that is the form in which fuel use rises evenly with distance. The trip is then priced per litre, with the optional driving-style and conditions multipliers applied to every car. Formula: `L/100 km = 282.480936 ÷ mpg (UK); litres = L/100 km × style × conditions × km ÷ 100; cost = litres × price per litre` - The starting journey is 300 miles, which is 482.8 km. Our car starts at 38 mpg (UK) and The big one at 25 mpg (UK); both start at the Government weekly average of 1.7278 per litre. - The imperial gallon is taken as 4.54609 litres, about 20% bigger than a US gallon, so a UK mpg figure is not comparable with an American one. - The electric car is set to use 17 kWh per 100 km, priced at a placeholder £0.30 a kWh. Swap in your home or public charging tariff. - Petrol is counted at 2.31 kg of CO₂ per litre and diesel at 2.68. Electricity uses a grid figure that starts at 300 g per kWh. ## How to use the fuel cost calculator 1. **Check the units.** The UK set is miles, litres and mpg (UK). Open Units to switch to imperial gallons or kilometres; typed numbers convert as you switch. 2. **Set the journey.** Type the miles, how many people share the car, and choose One way or the return leg. Pounds are already selected in the currency box. 3. **Pick how you drive.** Motorway cruising at 70 mph costs more than steady running, and a cold morning costs more again. Choose both in the two drop-downs. 4. **Price each car.** Open Compare vehicles, enter each car’s mpg and your local price per litre, and add a diesel or electric model with Add vehicle. 5. **Read the gap.** The table lists cost, litres and CO₂ per car. Trips like this per year turns the gap between the cheapest and dearest into a yearly figure. ## Example: 300 miles in a 38 mpg car, a 25 mpg car and an EV A 300-mile trip is 482.8 km. At 38 mpg (UK) the car needs 35.89 litres: £62.01 at the DESNZ average of 1.7278 per litre on 2 November 2026, so £31.01 each for 2 people, with 82.9 kg of CO₂. The 25 mpg car needs 54.55 litres and costs £94.26. The electric car uses 82.08 kWh at £0.30, which is £24.62, or £69.63 less than the 25 mpg car. Twelve such trips save £835.61. ## When to use the fuel cost calculator - **Motorway run to see family.** Enter the miles and passengers, then read what each person owes toward the petrol on a 300-mile weekend away. - **Comparing a diesel estate with a hatchback.** Add both cars with their mpg and the diesel and petrol pump prices to see which is cheaper for the same journey. - **Testing an electric car.** Add an Electric vehicle with your home tariff in pounds per kWh and compare its trip cost with the petrol cars. - **Turning mpg into litres.** Type an mpg (UK) figure and read the litres per 100 km shown beside it before you compare with a continental brochure. ## What the fuel cost calculator does not do - The style and condition factors are rough multipliers applied equally to every vehicle. They are not measurements of your car. - Costs cover fuel or electricity only: no tolls, parking, wear, depreciation or charging losses beyond the consumption you enter. - Each vehicle has one fuel price and the CO₂ figures are tailpipe estimates from fixed constants, with a single grid intensity for all electric vehicles. - The cost split between passengers is always equal, and hybrids and plug-ins are not modelled. - Settings are not saved; reloading restores the three starting vehicles. The built-in pump price is a national average from an official page on the date shown, not the price at your station, and some countries have no single published average, in which case you enter it. ## When something else is a better fit - **When you do not know the distance yet and need a straight-line or road estimate**, use the [Distance Calculator](https://aumnitools.com/tool/distance-calculator.md). - **When you want fuel as one line in a whole trip budget**, use the [Trip Planner](https://aumnitools.com/tool/trip-planner.md). - **When you need real consumption for a particular route and load**, use your car's trip computer or a full-tank fill-up record. ## Questions about the fuel cost calculator ### How much does a 300-mile trip cost in a 38 mpg car? About £62.01. At 38 mpg (UK) the car uses 35.89 litres, priced at the 1.7278 per litre weekly average from 2 November 2026. Change the price to what your station charges and the figure follows. ### Is mpg (UK) the same as US mpg? No. An imperial gallon is 4.546 litres and a US gallon 3.785, so 40 mpg (UK) is only about 33 mpg on the US scale. This version assumes mpg (UK) unless you switch the units. ### Where does the starting pump price come from? It is the unleaded petrol average in the Government’s weekly road fuel prices, for 2 November 2026. It is a national average, not your local price, and it does not cover diesel. ### Can I price a diesel car? Yes. Type the diesel pump price into that car’s price box and set Fuel to diesel. Diesel counts as 2.68 kg of CO₂ per litre against 2.31 for petrol, but the price is only what you enter. ### How do I compare petrol with an electric car? Add a vehicle and switch it to Electric, then enter its kWh per 100 km and your tariff. At 17 kWh per 100 km and £0.30 a kWh the 300 miles cost £24.62, against £62.01 for the 38 mpg car. ## Related tools - [Distance Calculator](https://aumnitools.com/tool/distance-calculator.md): Great-circle distance, bearings and midpoint between two points or 32 cities - [Trip Planner](https://aumnitools.com/tool/trip-planner.md): Trip itinerary, budget per person and packing list, saved in your browser - [Unit Converter](https://aumnitools.com/tool/unit-converter.md): Converts 102 units in 11 categories, with temperature offsets and 0 to 12 decimals ## About this page Runs in your browser: what you enter is processed on this device and is not uploaded. Last checked against the tool's code on 2026-11-08. Interactive version: https://aumnitools.com/uk/tool/fuel-cost-calculator