How to Calculate Fuel Costs for a Journey in the UK: Step-by-Step Guide

Introduction

Running a car in the UK costs far more than fuel alone. Putting figures on each part of motoring makes it easier to budget, claim what you're owed and compare petrol, diesel and electric.

This guide explains how to calculate fuel Costs for a Journey in the UK, step by step. Calculate the petrol or diesel cost of any journey using UK miles per gallon. You'll see the formula, a fully worked example and practical tips for UK readers.

What this calculation covers

Calculate the petrol or diesel cost of any journey using UK miles per gallon.

Accurate motoring numbers help you budget journeys, claim mileage relief from HMRC and decide whether an electric car makes financial sense for you.

The method and formula

Divide miles by MPG to get gallons, convert to litres (1 UK gallon = 4.546 litres), then multiply by the price per litre.

Every figure on our fuel Cost Calculator follows this method, so you can check the working yourself.

Worked example

Here's a typical example using these figures:

Running them through the method gives:

The headline figure is fuel cost: £14.14. Change any input and the result will move with it.

How to use the calculator

1. Enter or choose journey distance (miles).
2. Enter or choose fuel economy (mpg).
3. Enter or choose fuel price (p/litre).
4. Read your results. The main figure is shown at the top, with a breakdown underneath.
5. Try different values to compare scenarios side by side.

Tips for UK readers

• UK MPG uses imperial gallons (4.546 litres), which differ from US gallons.
• HMRC's approved mileage rate is 45p per mile for the first 10,000 business miles.
• Home EV charging on an off-peak tariff is usually far cheaper than public rapid chargers.
• Depreciation is often the largest hidden cost of owning a newer car.

Frequently asked questions

What's the quickest way to work out fuel Costs for a Journey?

Use our free fuel Cost Calculator. It applies this method automatically: Divide miles by MPG to get gallons, convert to litres (1 UK gallon = 4.546 litres), then multiply by the price per litre.

What MPG should I use?

Use your real-world figure from your car's trip computer if you can; official figures are often optimistic.

Can I claim for commuting miles?

No. Normal commuting to a permanent workplace doesn't count as business mileage.

How often do HMRC mileage rates change?

Rarely. The 45p rate has been unchanged for many years, but always check GOV.UK.

Summary

To work out fuel Costs for a Journey, follow the method above: Divide miles by MPG to get gallons, convert to litres (1 UK gallon = 4.546 litres), then multiply by the price per litre. For a quick, accurate answer with your own figures, use the calculator.

Next, read Fuel Costs for a Journey: Common Mistakes, Tips and FAQs.