What Does the Cost Per Mile Calculator Do?
A fuel cost per mile makes vehicles and journeys easier to compare. Pump prices are quoted per litre in the UK while many drivers know their car's economy in miles per imperial gallon. The calculator joins those units and gives a pence-per-mile result, with equivalent costs for longer distances. It is especially useful for answering a small practical question such as how much fuel an extra 100-mile journey will use.
How to Use This Calculator
- Find a representative fuel-economy figure in imperial MPG. Use a full-to-full measurement or an appropriate long-term display average, and avoid mixing US gallons with the UK figure expected by this tool.
- Enter the retail pump price in pence for one litre. Type 145 for £1.45, not 1.45. If comparing petrol with diesel, calculate each vehicle using the relevant fuel price rather than assuming both fuels cost the same.
- Calculate and read the pence-per-mile figure alongside the cost of longer distances. The longer-distance amounts make rounding easier to interpret when a single mile costs only a fraction of a pound.
- Repeat with another MPG or pump price. Keep a note of which assumption changed so that a lower number can be attributed to better economy, a cheaper price or both.
The Maths & Assumptions Behind the Tool
One mile consumes 1 ÷ MPG imperial gallons. Multiplying by 4.54609 converts that quantity to litres. Multiplying by pence per litre gives pence per mile directly. To price a route, multiply by miles and divide by 100 for pounds. The model has no fixed-cost component: under its constant-consumption assumption, a 100-mile journey costs exactly ten times a ten-mile journey before display rounding.
Worked example
At 45 MPG and 145p/litre, fuel costs approximately 14.65p per mile (14.6p when rounded to one decimal place).
Why This Matters for UK Drivers
The result covers fuel consumption at the MPG and price entered. It is not an all-in ownership rate, a recommended car-sharing contribution or an approved business mileage allowance. A car with cheap fuel can still be expensive once insurance, repairs, depreciation and finance are counted. Likewise, an employer's reimbursement rate can cover a different set of costs. Keep the description attached to the number so a fuel-only result is not later mistaken for a complete motoring cost.
For two cars, use the same measurement basis and prices that each vehicle will actually pay. A diesel and petrol comparison may need different pump prices. Compare a motorway trip with motorway economy rather than a cold urban average. The output also gives fuel volume per distance, which separates consumption from price: if expenditure rises while litres per mile stay unchanged, the price input rather than vehicle efficiency explains the difference.
Interpreting the result in practice
A pence-per-mile figure is useful for a budget but should not be confused with a measured marginal cost for every individual mile. A cold start, congestion or a steep route can make one short trip much less economical than a long-run average. For regular short journeys, use an MPG figure measured on those journeys. For a different trip, run a separate scenario rather than presenting the annual average as a guarantee.
Consider a price change from 145p to 155p per litre with unchanged economy. The fuel bill increases by 155 divided by 145, or approximately 6.9%. The extra cost over a chosen distance can be found by subtracting the two calculator results. This is a clearer way to judge the household impact of a pump-price rise than looking at the price of a full tank, which also depends on how much fuel was already present.
For a route of 80 miles, a fuel rate of 15p per mile gives £12. That multiplication is useful when comparing an extra trip with another travel option, but retain the word fuel on the result. Parking or a bridge charge should be added as separate trip costs. If the competing option is a rail ticket, compare the complete return itinerary and number of travellers before deciding which total is smaller.
Frequently asked questions
Does this include depreciation, tyres or servicing?
No. It is fuel-only cost per mile.
Can I use diesel?
Yes. Enter the diesel price you pay and the vehicle's real MPG.
Using pence per mile properly
What the number tells you
Fuel cost per mile is a useful common unit because it lets you compare different cars and different fuel prices on the same basis. It also makes ad-hoc journeys easier to price: multiply the pence-per-mile result by the distance you expect to drive.
Use realistic inputs
For the most meaningful result, use real-world MPG rather than an official laboratory figure. A vehicle that achieves 45 MPG in daily use should be compared at 45 MPG even if its published figure is higher. Current pump price matters too, especially when comparing petrol and diesel vehicles.
What is outside the calculation
This is fuel cost per mile, not total ownership cost per mile. Insurance, tax, servicing, tyres, finance and depreciation are excluded. For reimbursement or a whole-life vehicle comparison, those costs may be as important as fuel.