Auto & Travel · 1 min read
How to calculate fuel economy and trip cost
Fuel economy is distance divided by fuel. Once you know it, trip cost is one more step.
Last updated November 3, 2026
Measure miles per gallon
Fill the tank, reset the trip meter, drive as normal, then fill the tank again and note the gallons added.
Formula
mpg = miles driven ÷ gallons used
Worked example
360 miles on 12 gallons
Result: 360 ÷ 12 = 30 mpg
Tip
Averaging over several fill-ups is more reliable than one.
Estimate trip cost
Formula
cost = (distance ÷ mpg) × price per gallon
Worked example
A 300-mile trip at 30 mpg
| Step | Calculation | Value |
|---|---|---|
| Gallons used | 300 ÷ 30 | 10 gallons |
| Cost | 10 × 3.50 dollars | 35 dollars |
Result: 35 dollars at 3.50 dollars a gallon
Metric equivalents
Outside the US, economy is usually given as liters per 100 km, where lower is better.
Formula
L/100 km = 235.215 ÷ mpg
So 30 mpg is about 7.8 L/100 km.