What is the MPG Calculator?
Calculate your car’s real fuel economy from miles driven and gallons used. Calculating real-world miles per gallon from your own fill-ups is more accurate than the dashboard estimate and can reveal maintenance problems.
How to use the MPG Calculator
- Enter your miles driven, your gallons used.
- Results update automatically as you type; you can also press Calculate.
- Read the output: fuel economy, l/100 km, km/l.
- Use the 📊 chart to see the result visually, then copy or share it.
Formula and method
Worked example
With miles driven = 340, gallons used = 11.6, the MPG Calculator returns fuel economy: 29.31 mpg; l/100 km: 8.02; km/l: 12.46.
Where the MPG Calculator helps in real life
You filled the tank, drove 342 miles and refilled with 11.4 gallons. The calculator gives your actual MPG to compare with the official rating.
Your fuel economy seems worse than last month. Tracking MPG over a few tanks can reveal under-inflated tires or other issues.
Common mistakes to avoid
- Relying only on the dashboard estimate.
- Calculating after a partial fill.
- Comparing a winter tank with a summer tank.
- Judging economy from a single tank.
💡 Practical tip: A sudden drop in MPG can be an early sign of low tire pressure or a maintenance problem.
Tips for better results
- Fill to the same point each time.
- Average three or more tanks.
- Check tire pressure monthly.
Frequently asked questions
What does the MPG Calculator do?
Calculate your car’s real fuel economy from miles driven and gallons used.
How is it calculated?
The MPG Calculator uses this method: MPG = Miles ÷ Gallons.
Can you show an example?
With miles driven = 340, gallons used = 11.6, the MPG Calculator returns fuel economy: 29.31 mpg; l/100 km: 8.02; km/l: 12.46.
Is the MPG Calculator accurate?
Yes. It uses standard formulas and exact constants, and the results are verified by our automated test suite. Values are displayed to up to 12 significant digits.
Is this tool free and private?
Yes — the MPG Calculator is completely free with no sign-up, and it runs entirely in your browser, so the values you enter are never uploaded to our servers.
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