Free calculator
Gas mileage calculator (MPG & l/100 km)
Enter the distance you drove and the fuel you put in at the next fill-up. You get your MPG, the metric equivalent and the cost per 100 miles.
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Average fuel consumption
27.8MPG
- 8.5l/100 km
- 11.8km/l
- $36.23fuel cost
- $11.32per 100 miles
Carage logs every fill-up and works out your real average consumption and running costs automatically. Try it free
How to calculate gas mileage
Fill the tank to full and note the odometer (or reset the trip meter). Drive as usual, then fill the tank again and note how many gallons it took. MPG = miles driven ÷ gallons used. For example, 320 miles on 11.5 gallons is 27.8 MPG.
In countries that use the metric system, consumption is given as litres per 100 km: l/100 km = litres used ÷ kilometres driven × 100. To convert, divide 235.2 by the figure: 27.8 MPG (US) ≈ 8.5 l/100 km. A UK (imperial) gallon is bigger, so the same car shows about 20% more MPG in the UK.
Why your MPG differs from the sticker
Short trips, cold weather, highway speed, tyre pressure, roof boxes and heavy loads all raise consumption. Measuring over several full tanks gives a much more honest average than a single fill-up.
Track it automatically
Get your real average, not just one tank
Log each fill-up in Carage
Odometer, gallons and price take a few seconds.
Fill to full now and then
Carage measures consumption between full tanks.
Watch the trend
Average MPG, fuel cost per month and cost per mile, updated with every fill-up.
Gas mileage questions
What is good gas mileage?
It depends on the vehicle: many compact cars manage 30–40 MPG, midsize SUVs 22–30 MPG and pickups less. Compare against your own average over time rather than other cars.
How do I convert MPG to l/100 km?
Divide 235.2 by the US MPG figure (282.5 for UK MPG). 30 MPG (US) is about 7.8 l/100 km.
Why calculate over several tanks?
Pumps shut off at slightly different levels, so a single tank can be off by several percent. Averaging over multiple full tanks smooths that out.
Does the calculator save my data?
No. It runs in your browser session and stores nothing. To keep a history of fill-ups, use the Carage app.
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Carage is available for iPhone and iPad. Scan the code or open this page on your iPhone.