Fuel Economy Calculator

How UK fuel economy is calculated

• MPG (imperial) = miles driven ÷ imperial gallons used.
• 1 imperial gallon = 4.54609 litres (not the US gallon of 3.78541 litres).
• L/100km = 282.481 ÷ imperial MPG (lower is better).
• km/L = imperial MPG × 0.354006.
• Total fuel cost = imperial gallons used × price per gallon.
• Cost per mile = total fuel cost ÷ miles driven.

UK forecourts price fuel in pence per litre, but economy is traditionally quoted in MPG using the imperial gallon. For the most accurate reading, measure miles and fuel between two brim-full fill-ups. Smooth driving, correct tyre pressure and less idling all improve economy.

Frequently Asked Questions

How do I calculate MPG in the UK?

UK miles per gallon = miles driven ÷ imperial gallons used. For example, 300 miles on 12 imperial gallons is 25 MPG. The UK uses the imperial gallon (4.54609 litres), so UK MPG figures are higher than US MPG for the same car.

How is the imperial gallon different from the US gallon?

The imperial gallon is 4.54609 litres, while the US gallon is only 3.78541 litres. Because the imperial gallon is about 20% larger, UK MPG values are roughly 20% higher than US MPG for the same fuel economy.

How do I convert MPG to L/100km?

For imperial MPG, L/100km = 282.481 ÷ MPG. So 25 imperial MPG ≈ 11.30 L/100km. A lower L/100km number means better economy, the opposite of MPG.

What is cost per mile?

Cost per mile = total fuel cost ÷ miles driven, where total fuel cost = imperial gallons used × price per gallon. It is a quick way to budget journeys.