Tracking your vehicle's gas mileage is one of the most effective ways to monitor its mechanical health, budget for regular driving costs, and reduce your carbon footprint. Fuel economy measures exactly how far a vehicle can travel per unit of fuel consumed. Because driving styles and tire inflations change mileage efficiency, calculating your true average MPG over time provides far more accurate budget data than relying strictly on manufacturer specifications.
To measure mileage manually, fill your gas tank completely and record the starting odometer reading. Drive normally until you need fuel again.
At the next fill-up, fill the tank completely and record both the ending odometer reading and the exact number of gallons (or liters) filled. Subtract the start odometer from the end odometer to find the distance. Divide this distance by the fuel volume to calculate miles per gallon (MPG). To convert distance to kilometers or volume to liters, check out our translating measuring units tool.
To estimate total trip costs from your calculated mileage, use our dedicated estimating transport gas costs tool. For checking basic arithmetic, use our standard daily math helper.
While the US and UK use miles per gallon (MPG) where higher numbers represent better efficiency, most other countries use liters per 100 kilometers (L/100km), where lower numbers represent better efficiency.
Converting between them uses the constant: MPG = 235.215 / (L/100km). For example, a car that consumes 8 liters per 100km has a mileage of 235.215 / 8 = 29.4 MPG. Our online tool converts between these units automatically.
Understanding fuel economy helps in planning long-distance road trips, allowing you to estimate how many fuel stops are necessary and the total volume of fuel you will purchase. It is also beneficial for tracking seasonal changes, as cold weather, winter fuel blends, and frequent use of air conditioning can decrease your overall fuel efficiency.
Suppose you fill your tank and record an odometer reading of 45,200 miles. At the next fill-up, the odometer reads 45,550 miles, and you fill exactly 12 gallons of gas.
First, calculate the distance driven: 45,550 - 45,200 = 350 miles. Next, calculate the mileage: divide distance by gallons: 350 miles / 12 gallons = 29.17 MPG. The vehicle achieved an average of 29.17 miles per gallon over that tank. This example shows how simple odometer and pump receipts establish exact vehicle efficiencies.