US gas cost formula: miles, MPG and dollars
For an American road trip, US gallons needed = miles driven ÷ US MPG. Multiply the gallons by the pump price per US gallon to estimate fuel cost. The calculator defaults to US MPG, which differs from British imperial MPG because the gallon sizes are not the same.
Example: 280 miles, 28 US MPG, $3.50 per gallon
280 ÷ 28 = 10 US gallons; 10 × $3.50 = $35.00. The gas price is an example and not a live pump quote. Speed, weather, traffic and vehicle load affect real consumption.
British MPG versus US MPG
An imperial gallon is 4.54609 liters. A US liquid gallon is 3.785411784 liters. A British MPG figure cannot be used directly as US MPG; select the conversion mode to avoid unit errors.
Frequently asked questions
Does the calculator include tolls or parking?
No, only the estimated amount paid for gas.
What should I enter for a round trip?
Use the total mileage for both directions.