How to use this calculator
Fill your tank completely, reset your trip odometer, then drive normally until you need gas again. At the pump, note how many gallons it takes to fill up and how many miles you drove. Enter both numbers above.
For cost estimates, enter the current gas price per gallon and your average weekly driving distance. The calculator will project your monthly and annual fuel expenses at your actual MPG.
The calculator also converts your MPG to liters per 100 kilometers for international comparison. Lower L/100km numbers mean better efficiency (the opposite of MPG where higher is better).
Factors that affect your gas mileage
Your real world MPG depends on driving style, terrain, weather, and vehicle condition. Highway cruising at 55 to 65 MPH is the sweet spot for most vehicles. Above 65, aerodynamic drag increases significantly and fuel economy drops.
Cold weather reduces fuel economy because engines take longer to warm up, winter fuel blends have less energy, and tire pressure drops in cold air. Expect 10% to 20% lower MPG in winter compared to summer.
Vehicle maintenance matters more than most drivers realize. A clogged air filter, worn spark plugs, or low tire pressure can each reduce MPG by 1% to 4%. Combined, deferred maintenance can cost you 10% or more of your fuel efficiency.
Frequently asked questions
What is considered good gas mileage?
For a standard sedan, 30 MPG or higher is good. SUVs doing 25+ MPG are above average. Trucks at 20+ MPG are solid. Hybrids typically achieve 40 to 60 MPG. The national average for new vehicles in 2024 is about 26 MPG combined.
How can I improve my MPG?
Drive at steady speeds and avoid hard acceleration. Keep tires at the recommended pressure. Remove unnecessary weight from your vehicle. Use cruise control on highways. Stay current on maintenance including air filters, spark plugs, and oil changes. Avoid excessive idling.
Why is city MPG lower than highway MPG?
City driving involves constant stopping and starting, idling at red lights, and low speed acceleration. All of these burn extra fuel. Highway driving at a steady speed keeps the engine in its most efficient operating range. Most cars get 20% to 30% better MPG on the highway.
When should I worry about MPG dropping?
A sudden drop of 3+ MPG below your normal average suggests a maintenance issue. Check your tire pressure, air filter, and spark plugs first. A faulty oxygen sensor or fuel system problem can also cause sudden efficiency drops. Gradual changes of 1 to 2 MPG between seasons are normal.