How to Work Out MPG
Use this simple step-by-step method to calculate your real-world fuel economy accurately.
Last updated: 6 April 2026
Quick Answer
MPG formula: MPG = miles driven ÷ gallons used
If your fuel receipt is in litres, convert first: UK gallons = litres ÷ 4.54609
Step-by-Step: How to Work Out MPG
The most accurate MPG reading comes from measuring a full tank cycle rather than using a dashboard estimate.
1) Fill the tank and reset your trip meter
Fill up until the pump clicks off, then reset your trip odometer to zero.
2) Drive as normal
Use your usual routes and driving style. This gives a realistic MPG figure for your day-to-day driving.
3) Refill and record fuel used
At your next fill-up, note the miles on your trip meter and the litres added.
4) Convert litres to UK gallons
Use: UK gallons = litres ÷ 4.54609.
5) Calculate MPG
Use: MPG = miles ÷ UK gallons.
Worked Example (UK MPG)
Say you drove 287 miles and needed 32 litres to refill:
- Convert litres to UK gallons: 32 ÷ 4.54609 = 7.04 gallons
- Calculate MPG: 287 ÷ 7.04 = 40.8 MPG
Your real-world fuel economy is 40.8 UK MPG.
Common Mistakes That Give the Wrong MPG
- Mixing up UK gallons and US gallons
- Not filling to full at both the start and end
- Using very short trips only (cold engine bias)
- Rounding fuel values too early
How to Get a More Accurate Average
Track MPG over 3 to 5 full tanks and take the average. One tank can be distorted by weather, traffic, or motorway-heavy driving.
Skip the Manual Maths
Enter your miles and fuel used and we will calculate MPG instantly.
Try the MPG CalculatorFrequently Asked Questions
What is the formula to work out MPG?
MPG = miles driven ÷ gallons used. If fuel is in litres, convert to gallons first.
How do I work out MPG from litres in the UK?
Divide litres by 4.54609 to get UK gallons, then divide miles by that value.
Is dashboard MPG accurate?
It is useful as a guide, but fill-to-fill calculations are usually more accurate for true real-world MPG.