A 10 mpg difference is worth more than it sounds. Over 10,000 miles a year, a 45 mpg car uses about 63 fewer gallons than a 35 mpg car, which works out at roughly £430 a year if fuel costs £1.50 a litre, and more if prices rise.

How do you work out the cost of 10 mpg?

Divide your yearly mileage by the car's mpg to get the gallons you use. Multiply by 4.546 to convert gallons to litres, then multiply by the price per litre. Doing the sum for two cars shows the difference in pounds.

What does the difference look like over a year?

This example uses 10,000 miles a year and a fuel price of £1.50 a litre. Your own figures will differ, so swap in your mileage and the price you pay.

35 mpg car: about 286 gallons, roughly £1,948 a year
45 mpg car: about 222 gallons, roughly £1,515 a year
Difference: roughly £433 a year, or about £36 a month

At £1.70 a litre, the same gap grows to roughly £491 a year.

Why does the official mpg figure differ from what you get?

Official figures come from standard laboratory tests. Real-world economy depends on your journeys, speed, traffic, weather, tyre pressures and how the car is loaded. Your trip computer, or a simple brim-to-brim check at the pump, gives a better picture of what your car actually does.

Which changes make the biggest difference?

Mostly town driving: a hybrid often does well in stop-start traffic.
Long motorway runs: an efficient diesel or petrol can return good economy at steady speeds.
Oversized car: moving to a smaller, lighter car you still fit in can make a noticeable difference.
Home charging available: an electric car can cost less per mile, as our guide to used electric car running costs explains.

Is it worth changing car just to save fuel?

Not always. Compare the fuel saving with the cost of changing, including any difference in price, tax and insurance. Our cost comparison calculator helps you weigh it up, and our guide on when it is time to change your car covers the signs to look for.

Can you improve mpg without changing car?

Yes. Keep tyres at the right pressure, take out unnecessary weight, drive smoothly, and keep the car serviced. Our guide to spending less on fuel has more tips.

Common questions

Is a 5 mpg difference worth bothering about?

It depends on your mileage. The more you drive, the more any gap adds up.

Does mpg matter for electric cars?

Electric cars use miles per kWh instead. The idea is the same: the more efficient the car, the less each mile costs.

Do higher-mpg cars always cost less to run?

Not necessarily. Tax, insurance, servicing and depreciation also count, so look at the full picture.

Find an efficient car in Barnsley

Browse our used cars or visit anycolourcar.com in Barnsley, South Yorkshire. Call Sales on 01226 574410. To see what your current car is worth, try our valuation page.

This guide is general information, not financial advice. Updated October 2026.

How Much Does 10 MPG Really Cost You? A Worked Example