About fuel economy
This gas mileage calculator turns a distance and the fuel used into your fuel economy, shown as miles per gallon (US or UK), litres per 100 km and kilometres per litre, so you can compare figures whatever units you use. It runs in your browser; nothing is uploaded.
How Gas Mileage works
The formula
MPG = miles driven ÷ gallons used. L/100km = litres used ÷ kilometres driven × 100. km/L = kilometres ÷ litres. A US gallon is 3.785 L; a UK (imperial) gallon is 4.546 L, so UK MPG figures look higher.
Worked example
You drove 300 miles on 12 US gallons: MPG = 300 ÷ 12 = 25 MPG. That is about 9.4 L/100km, or roughly 10.6 km/L.
Common uses
- Calculate MPG from a fill-up
- Convert between MPG and L/100km
- Compare US and UK gallons
- Check a car fuel economy
- Track fuel efficiency over time
- Compare two vehicles
- Estimate running costs
- Work out km per litre
Frequently asked questions
How do I calculate gas mileage?
Divide the miles driven by the gallons of fuel used. 300 miles on 12 gallons is 25 MPG.
What is the difference between US and UK MPG?
A UK gallon is larger (4.546 L vs 3.785 L), so the same car shows a higher MPG in UK figures.
How do I convert MPG to L/100km?
Lower L/100km means better economy; the tool shows both at once from the same numbers.
Can I use kilometres and litres?
Yes — switch to the metric tab and enter km and litres.
Is my data uploaded?
No — it calculates in your browser.
Is it free?
Yes, completely free.