How to calculate MPG
- Fill the tank and reset your trip meter (or write down the odometer).
- Drive normally until you need fuel again.
- Fill the tank and note the gallons the pump shows.
- Divide the miles driven by the gallons.
Example: 312 miles on 10.4 gallons is 30 MPG, which is 7.84 L/100 km. At $3.25 a gallon, each mile costs about 10.8¢, or $10.83 per 100 miles.
Why your MPG differs from the sticker
Official ratings come from standard lab tests. Real mileage drops with short trips, cold weather, highway speeds above 60 mph, idling, roof racks and under-inflated tires. Averaging three or four fill-ups gives a truer number. To compare with your car's official rating or plan a trip, use the fuel cost calculator, which looks up the EPA figures for your exact car.
Fuel cost per 100 miles
Cost per 100 miles = 100 ÷ MPG × price per gallon.
| MPG | $3.00/gal | $3.50/gal | $4.00/gal | $4.50/gal |
|---|---|---|---|---|
| 15 | $20.00 | $23.33 | $26.67 | $30.00 |
| 20 | $15.00 | $17.50 | $20.00 | $22.50 |
| 25 | $12.00 | $14.00 | $16.00 | $18.00 |
| 30 | $10.00 | $11.67 | $13.33 | $15.00 |
| 35 | $8.57 | $10.00 | $11.43 | $12.86 |
| 40 | $7.50 | $8.75 | $10.00 | $11.25 |
| 50 | $6.00 | $7.00 | $8.00 | $9.00 |
At $3.50 a gallon and 12,000 miles a year, moving from a 20 MPG vehicle to a 30 MPG one saves about $700 a year.
Frequently asked questions
How do I calculate gas mileage?
Divide the miles you drove by the gallons it took to refill. 280 miles on 8 gallons is 35 MPG.
How do I convert MPG to L/100 km?
Divide 235.215 by the MPG. 25 MPG is 9.41 L/100 km. Lower L/100 km means better economy.
Should I use the trip computer's MPG?
It's handy, but many read a few percent high. The fill-up method uses what you actually paid for.
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