This gas mileage calculator computes MPG from miles driven and gallons used. Enter the trip odometer distance and the gallons it took to refill. The result is miles per gallon for that tank or trip segment.
Drivers use it to verify trip computer claims, compare summer versus winter tanks, or check whether a repair changed efficiency.
Worked example
Example with defaults: 300 miles and 10 gallons. MPG = 30.
| Input | Value |
|---|---|
| Miles | 300 |
| Gallons | 10 |
| MPG | 30 |
Fill up method
- Fill the tank and reset a trip meter, or note the odometer.
- Drive normally until the next fill.
- Fill again and record gallons pumped.
- Divide miles by gallons.
Partial fill ups make MPG noisier. Full to full is cleaner.
US MPG versus L/100 km
This tool returns MPG. To talk in L/100 km, convert with a standard factor after you have MPG. Do not mix litre amounts in the gallons field without converting.
Comparing vehicles
Use the same driving mix when you compare two cars. City only tanks look worse than highway tanks for most vehicles.
Once you know MPG, estimate trip spend with the fuel cost calculator. Reimbursement planning belongs on the mileage reimbursement calculator.
Common mistakes
- Using litres in the gallons box
- Forgetting to reset the trip meter
- Comparing one city tank to one highway tank as if they were equal
Seasonal swings
Winter blends, cold engines, and short trips lower MPG. Compare tanks from similar weather before judging a repair.
Tire pressure and load
Low pressure and heavy cargo reduce efficiency. Check those before you assume the engine is at fault.
Tracking habit
Log date, miles, gallons, and notes. Patterns appear faster than one off tanks.
Practical planning tips
Write down the inputs you used so you can repeat the estimate later. Small changes in rate, depth, hours, or price can move the result more than people expect.
When you compare two options, change one variable at a time. That keeps the comparison honest and easy to explain to a partner, client, or lender.
Units and rounding
Keep units consistent across every field. Mixing inches with feet, litres with gallons, or monthly figures with annual figures is the most common source of wrong answers.
Round only at the end for ordering or payments. Early rounding in each step can stack into a surprising gap versus the live calculator.
What this estimate does not include
Taxes, delivery fees, labor, penalties, and one time service charges are often outside the core formula. Add those on paper when you build a real budget.
Local rules, code requirements, and lender overlays can still change the final decision even when the math is correct.
How to double check the result
Recalculate once with a pencil using the same formula shown on this page. If your manual result is close to the tool, your inputs are probably consistent.
If the two answers diverge, check the field labels again before you trust either number for spending or filing.
When to get a second opinion
Large purchases, structural work, medical or legal questions, and loan contracts deserve a qualified human review. Use this page to prepare better questions, not to replace that review.
Save a screenshot or note of the inputs and result date. That record helps when you talk with a contractor, accountant, or lender later.