Gas Mileage Calculator (MPG)
Measure your car's real fuel economy from one full tank and convert it between mpg and L/100 km.
- US mpg—
- UK mpg—
- Liters per 100 km—
- Kilometers per liter—
- Fuel cost per distance—
Saved scenarios
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Estimates for education only — not financial, tax or legal advice. Lenders may calculate taxes and fees differently by state or province. Always check your contract.
How to calculate your gas mileage
- Fill the tank completely and reset the trip meter.
- Drive normally until you need fuel again.
- Fill up again and note the gallons (or liters) added and the miles (or km) on the trip meter.
- Enter both numbers here.
Worked example
You drove 350 miles and needed 11.2 gallons to fill up: your car gets 31.3 mpg, which is 7.53 L/100 km, 13.3 km per liter or 37.5 UK mpg.
Why your mpg differs from the sticker
Real-world fuel economy depends on speed, traffic, temperature, tire pressure and load. Measuring over two or three full tanks gives the most reliable number. Use it in the fuel cost calculator to price your next trip.
Frequently asked questions
How do I calculate mpg?
Divide the miles driven by the gallons used to refill the tank. For example, 350 miles ÷ 11.2 gallons = 31.3 mpg.
How do I convert mpg to L/100 km?
Divide 235.215 by the US mpg figure. 30 mpg is about 7.8 L/100 km.
Why is UK mpg higher than US mpg?
A UK (imperial) gallon is about 20% larger than a US gallon, so the same car shows a higher mpg in the UK.
What is good gas mileage?
It depends on the vehicle. Many compact cars get 30–40 mpg on the highway, while large SUVs and pickups often get 15–25 mpg.
Is the trip computer accurate?
It is usually close but can be a few percent optimistic. Measuring at the pump is the most reliable method.
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