Gas Mileage Calculator
Gas mileage measures the distance a vehicle travels per unit of gasoline consumed. Use this free calculator to determine your car’s true miles per gallon (MPG), fuel cost per mile, and total fuel expense from your trip odometer reading and gas pump refill receipts.
Calculate Car Gas Mileage
Input distance driven and gallons added to refill your gas tank
From your trip odometer reading between fill-ups.
Shown directly on your gas station fuel pump receipt.
Traveling 30.00 miles for every gallon of gas consumed.
The Gas Mileage (MPG) Formula & Worked Example
Understanding how miles per gallon and fuel cost per mile are mathematically calculated
For metric drivers, fuel efficiency is expressed in liters per 100 km (L/100km) or kilometers per liter (km/L). You can calculate or convert metric figures using our Fuel Consumption Calculator.
Planning a road trip budget? Calculate point-to-point gasoline costs with our Fuel Cost Calculator.
How to Obtain Reliable Real-World Fuel Economy Measurements
Eliminating pump shutoff errors and driver measurement bias
Many drivers rely on their vehicle's digital dashboard computer to estimate gas mileage. However, automotive testing by the U.S. Department of Energy (FuelEconomy.gov) and engineering benchmarks show that in-dash displays frequently read 2% to 5% optimistic because they estimate fuel flow through injector pulse durations rather than measuring actual pumped volume.
To achieve accurate, repeatable gas mileage figures using manual pump measurements:
Calculating gas mileage after driving only 30 to 50 miles magnifies nozzle shutoff variation. A 0.5-gallon pump shut-off difference over 40 miles distorts calculated MPG by over 20%. Always drive at least 150 to 300 miles before refilling.
Dispenser flow rates, fuel temperature, foaming, and ground level affect when the nozzle clicks off. Refill at the same gas station and pump when possible, hold the handle at medium speed, and never "top off" past the first automatic shut-off click.
Individual tank runs vary with wind, weather, payload, and city-versus-highway ratios. Summing total miles across three tanks and dividing by total gallons pumped produces an accurate rolling average that reflects true real-world driving.
Rounding intermediate math introduces rounding drift. See AutoFuelCalc’s Calculation Methodology to see how our calculation engines enforce exact double-precision floating-point arithmetic.
If you prefer tracking mileage using cumulative odometer readings instead of trip meters, use our Real-World Full-Tank Odometer Tool.
Gas Mileage & Fuel Cost Per Mile Reference Table
Comparison of common MPG ratings, metric equivalents, and fuel cost per mile at benchmark gas prices
| Gas Mileage | Metric Equivalent | Cost @ $3.20/gal | Cost @ $3.60/gal | Cost @ $4.00/gal | Typical Vehicle Class |
|---|---|---|---|---|---|
| 20.0 MPG | 11.76 L/100km | $0.160 / mi | $0.180 / mi | $0.200 / mi | Full-size Pickup / V8 SUV |
| 25.0 MPG | 9.41 L/100km | $0.128 / mi | $0.144 / mi | $0.160 / mi | Mid-size Crossover / Minivan |
| 30.0 MPG | 7.84 L/100km | $0.107 / mi | $0.120 / mi | $0.133 / mi | Compact SUV / Sedan |
| 35.0 MPG | 6.72 L/100km | $0.091 / mi | $0.103 / mi | $0.114 / mi | Compact Hatchback / Sedan |
| 40.0 MPG | 5.88 L/100km | $0.080 / mi | $0.090 / mi | $0.100 / mi | Hybrid Crossover / Diesel Sedan |
| 50.0 MPG | 4.70 L/100km | $0.064 / mi | $0.072 / mi | $0.080 / mi | Compact Hybrid Sedan |
Gas Mileage vs. Fuel Economy vs. Fuel Consumption
While drivers frequently use these terms interchangeably, each has a specific definition in automotive engineering and consumer finance:
Gas Mileage
The everyday American consumer term describing how many miles a vehicle travels on one gallon of gasoline. It is mathematically synonymous with US MPG. You can convert between US and UK gallons using our MPG Calculator.
Fuel Economy
The formal regulatory and engineering term for distance traveled per volume of fuel (e.g., MPG, km/L). Higher numbers represent superior efficiency.
Fuel Consumption
The physical volume of fuel burned over a standard distance (e.g., liters per 100 km). Lower numbers represent higher efficiency. Check your metric consumption with our Fuel Consumption Calculator.
- Highway cruising speed and drag: Aerodynamic drag increases with the square of vehicle speed. Driving at 75 mph consumes 10% to 20% more gasoline than cruising at 55 to 60 mph.
- Underinflated tires: A 5 PSI drop below manufacturer recommendation increases rolling resistance, wasting roughly 2% to 3% of fuel.
- Cold weather & winter fuel blends: Winter gasoline contains more volatile butane and has roughly 1.5% to 2% less energy content than summer blends, while cold engines take longer to reach optimal thermal efficiency.
- Roof racks and excess cargo: External cargo boxes or bicycle racks create substantial turbulence, lowering highway MPG by 5% to 15%.
- Prolonged idling: Idling delivers exactly 0.0 MPG while burning 0.2 to 0.5 gallons of gasoline per hour.
Frequently Asked Questions
Compare trip costs, measure full tanks, or learn more About AutoFuelCalc.
Related Calculators
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Fuel Consumption Calculator
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Estimate total fuel required and gas expense for any road trip.
Fuel Cost Calculator
Calculate fuel cost per mile, per kilometer, and total journey cost.