How to Calculate the Gas Cost of a Road Trip (and Split It)
Before a road trip it helps to know what the fuel will cost — to budget, to compare driving with flying, or to split costs with friends. The math is simple once the units line up.
The formula
gallons = distance (miles) ÷ MPG and cost = gallons × price per gallon.
Example: 300 miles in a car that does 28 MPG with gas at $3.40/gallon → 10.7 gallons → about $36.43. Round trip: about $72.86. Split three ways: about $24.29 each.
The gas cost calculator does this in miles or kilometers, with prices per US gallon, UK gallon or liter, and adds tolls and parking to the split.
Fuel economy units
- MPG (US): miles per US gallon — higher is better.
- MPG (UK): miles per imperial gallon, about 20% larger than a US gallon, so UK MPG figures look higher for the same car.
- L/100 km: liters used per 100 km — lower is better. Common in Europe, Canada and Australia.
- km/L: common in Japan, Korea, Latin America and India.
Handy conversions: 28 US MPG ≈ 8.4 L/100 km ≈ 11.9 km/L. The calculator shows your figure in all units.
Getting a realistic MPG
Official ratings are measured in ideal conditions. Highway speed above about 60–65 mph, roof boxes, a loaded trunk, air conditioning and under-inflated tires all raise consumption. Your car's trip computer average over a few tanks is the most honest figure.
Splitting fairly
Common practice is to split fuel, tolls and parking equally among everyone in the car — sometimes including the driver, sometimes not, as a thank-you for driving. Agree before you leave.
Also splitting the restaurant bill? The tip calculator handles that.