Gas Mileage Calculator

About This Tool

The Gas Mileage Calculator helps you understand your vehicle's fuel efficiency and plan the fuel budget for any road trip. It operates in two modes. The Calculate MPG mode takes your fill-up data (miles driven and gallons used) and computes your actual miles per gallon, cost per mile, and total fuel expenditure. The Trip Planner mode estimates how much fuel and money a planned trip will require based on your vehicle's MPG and current gas prices.

How to Calculate MPG

Fill your tank completely. Reset your trip odometer. Drive normally until you need fuel again. Fill up completely and note how many gallons it took. Divide the miles driven by the gallons used. That is your actual MPG. Repeat this over several fill-ups for a more accurate average. Your real-world MPG will typically be 10-20% lower than the EPA estimate, depending on driving conditions and habits.

Factors That Affect Fuel Efficiency

Highway driving yields better MPG than city driving because constant speed is more efficient than frequent acceleration and braking. Aggressive driving (rapid acceleration, speeding, hard braking) can lower MPG by 15-30%. Proper tire inflation, regular maintenance, removing excess weight, and using cruise control all improve fuel economy. Air conditioning increases fuel consumption by 3-4%, while open windows at highway speeds create drag that has a similar effect.

Understanding Cost Per Mile

Cost per mile is the most practical metric for budgeting. If your vehicle gets 28 MPG and gas costs $3.50 per gallon, your fuel cost per mile is about $0.125. For a 12,000-mile annual driving average, that is roughly $1,500 per year in fuel alone. Improving your MPG by even 2-3 points through better driving habits can save $100-200 annually.