Gas Mileage Calculator

Use it when your task matches one of these common needs: Calculate MPG after filling a tank. Compare fuel use between trips or vehicles. It works best when you already know the miles driven and gallons used from the same fill-up, tank, or trip window.

In plain language: MPG = miles driven / gallons used. Gallons per 100 miles = gallons used / miles driven x 100. L/100 km uses the standard 235.214583 divided by MPG conversion. The examples on the page are there so you can compare your inputs with a fill-up example before copying the answer.

Miles driven: the odometer or trip-meter distance since the fill-up or route started. Gallons used: the fuel used for those same miles, usually the gallons added at the next fill-up. MPG: miles per gallon. Higher MPG means you went farther on each gallon. Gallons per 100 miles: fuel used per distance. Lower is better, and it can make savings easier to compare. L/100 km: the metric fuel-use version. Lower is better here too.

Read the headline answer, then check the smaller lines beside it. For everyday tools, those lines usually show the distance, time, cost, units, or setting that made the answer change.

One tank can be noisy. Pump shutoff, fill level, tire pressure, route, speed, weather, traffic, load, and driving style can all move the result. Also check that the odometer/trip meter and fuel amount cover the same window. For cleaner long-term MPG, average several tanks instead of trusting one unusual drive.

A full-tank fill-up is usually cleaner because the gallons added should match the miles driven since the last fill. A single trip can still work if you know the actual fuel used for that trip.

MPG is common in the United States, but gallons per 100 miles and L/100 km make fuel used per distance easier to compare. Lower is better for those two outputs.

Use this page to find fuel economy. Use the Fuel Cost Calculator when you already know the trip distance, MPG, and fuel price and want the money estimate.

The pump may stop at a slightly different fill level, the route may have more traffic, or the car may be carrying more weight. If one tank looks strange, average several normal fill-ups before deciding your MPG changed.

No. EPA labels are standardized estimates for comparing vehicles. This calculator shows your real fill-up math, which can be higher or lower because your route, speed, weather, tires, and driving style are different.

No. The math runs in your browser tab. Your miles, gallons, and recent results are not sent to a server.