MPG Calculator
Calculate your car's real-world fuel economy. Enter how far you drove and how much fuel you used, and we'll show your MPG in UK imperial, US, and L/100km — plus an estimated annual fuel cost.
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Calculate your MPG
How to calculate MPG
MPG (miles per gallon) measures how far your car travels on a single gallon of fuel. To calculate it yourself, fill your tank completely, reset your trip counter, and drive normally until you next fill up. Divide the miles driven by the gallons (or litres) used. Our calculator does the maths for you, converting between UK imperial gallons, US gallons, and litres automatically.
The formula for UK MPG is: Miles driven / (Litres used / 4.54609). For US MPG, replace 4.54609 with 3.78541 (the number of litres in a US gallon). For L/100km, the formula is (Litres used / (Miles x 1.60934)) x 100.
What is good MPG?
In the UK, a "good" MPG depends on your vehicle type. As a rough guide:
- Small cars(e.g. Fiesta, Corsa): 50–65 MPG
- Medium cars(e.g. Golf, Focus): 45–55 MPG
- Large cars / SUVs(e.g. Tucson, Qashqai): 35–50 MPG
- Performance cars: 25–35 MPG
Note these are UK imperial MPG figures. US MPG figures are roughly 17% lower because a US gallon is smaller than an imperial gallon. Real-world MPG is typically 10–20% lower than the manufacturer's official WLTP figure.
MPG vs L/100km
MPG and L/100km are two ways to express fuel efficiency. MPG is used in the UK and US — higher is better. L/100km is the standard in most of Europe and Australia — lower is better. Because the relationship is inverse, a car doing 50 UK MPG uses about 5.6 L/100km, while 30 UK MPG equals roughly 9.4 L/100km.
Be careful when comparing UK and US MPG. A UK imperial gallon is 4.546 litres, while a US gallon is only 3.785 litres. This means 40 UK MPG is equivalent to about 33 US MPG.
Frequently asked questions
How do I calculate MPG from litres?
Divide the miles driven by the litres used, then multiply by 4.54609 to get UK MPG, or by 3.78541 to get US MPG. For example, 300 miles on 40 litres = 300 / 40 x 4.546 = 34.1 UK MPG.
Why is my real MPG lower than the official figure?
Official WLTP fuel economy figures are measured under controlled lab conditions. Real-world driving involves cold starts, traffic, air conditioning, roof boxes, and varied speeds — all of which reduce efficiency. Most drivers see 10–20% worse than the official figure.
How can I improve my MPG?
Maintain steady speeds, avoid harsh acceleration and braking, keep tyres at the correct pressure, remove unnecessary weight and roof bars, and service your car regularly. Driving at 60 mph instead of 70 mph on the motorway can improve fuel economy by around 10%.
Does the Roadtrip app track my MPG?
Yes! The Roadtrip app calculates fuel costs for any journey using your exact car model and real-time fuel prices. Download it free to plan fuel-efficient road trips and track your spending.