Fuel & units

Cost per mile formula: a plain-English guide

By RoadCost Editorial4 min readUpdated 27 October 2026

Cost per mile is useful for commuting, business mileage and comparing two cars. The formula is simple, but it is easy to multiply the wrong numbers together. Fuel economy and fuel price do not sit in the same unit.

Quick answer

Cost per mile = total fuel cost ÷ miles driven. Find total fuel cost first: fuel used × price per unit. Do not multiply MPG by price per litre or gallon.

In this guide

1. The two-step method
2. A UK example
3. A US example
Questions

Key takeaways

Cost per mile needs total fuel cost first.
UK and US examples use different fuel units.
Fuel cost per mile is not the same as total ownership cost.

The two-step method

First, work out how much fuel the trip uses. Second, multiply by the price you pay. Then divide the total cost by the distance in miles.

This order prevents unit mistakes. If you start with MPG and price, you are mixing distance-per-fuel with money-per-fuel.

fuel used = distance ÷ MPG
fuel cost = fuel used × price per gallon
cost per mile = fuel cost ÷ miles

A UK example

Suppose a 100-mile trip uses 50 MPG UK and fuel costs 145p per litre. The trip uses about 9.09 litres. At £1.45 per litre, the fuel cost is about £13.18, or about 13.2p per mile.

The MPG figure is used to find litres, not multiplied by the pence-per-litre price.

A US example

Suppose a 300-mile trip uses 30 MPG US and fuel costs $3.50 per US gallon. The trip uses 10 gallons. The fuel cost is $35.00, or about 11.7 cents per mile.

The arithmetic is the same; only the fuel unit changes.

Questions

How do you calculate fuel cost per mile?

Divide the trip distance by MPG to get gallons, multiply by the price per gallon, then divide by the distance in miles.

What is cost per km?

It is total fuel cost divided by kilometres. Our calculators show both so you can compare across markets.

Does cost per mile include insurance and maintenance?

No. It is a fuel-only figure. Insurance, maintenance, depreciation and tolls are separate costs.

Sources

NIST — unit conversion — US customary and metric relationships used by the converters.
UK Weights and Measures Act 1985 — Statutory context for UK units, including the imperial gallon.
fueleconomy.gov — US fuel-economy ratings — EPA label values, test-cycle context and consumer guidance.
GOV.UK — weekly road fuel prices — UK price statistics for context, not a live station price.
US EIA — gasoline and diesel prices — US regional and national averages.

Try the calculator

Fuel cost calculator

Get total fuel cost, cost per mile and cost per km.

Related guides

Round-trip fuel cost formula

A simple method for round-trip fuel estimates, including detours, unit changes and the difference between one-way and return distance.

How much fuel does 100 miles use? A simple guide

Work out fuel use and fuel cost for 100 miles in UK or US units, with example tables and the formula behind the answer.

How to calculate commute fuel cost

A practical method for turning your daily commute into a fuel budget, including round trips, working weeks and real-world consumption.

A note on prices and rules

This guide explains arithmetic and units. It does not publish live fuel prices, electricity tariffs or changing tax rules. Use your own price and check official sources for anything that changes.

Page last reviewed: 27 October 2026. Formulas are covered by automated tests. Prices are inputs, not live data.