⛽MPG Calculator

This MPG calculator gives you an instant, accurate measure of your vehicle's fuel efficiency using nothing more than odometer readings and fill-up data. Miles per gallon is the standard measure of gas mileage in the United States, and knowing your real-world number helps you track vehicle health, budget fuel costs, and compare your car against EPA ratings. Enter the distance you drove and the fuel you used, and this miles per gallon calculator returns your MPG, its metric equivalent in liters per 100 kilometers, estimated cost per mile, and CO2 emissions for the trip.

How to Calculate Miles Per Gallon from a Fill-Up

The fill-up method is the most accurate way to measure real-world fuel economy from a tank. Start by filling your tank completely and resetting your trip odometer to zero. Drive normally through your usual mix of city and highway miles until the tank is substantially depleted. At your next fill-up, record the exact number of gallons added to refill the tank and the miles shown on your trip odometer. Divide the miles driven by the gallons added to get your MPG.

For example, if you drove 320 miles and the pump added 10.4 gallons, your gas mileage is 320 divided by 10.4, which equals 30.8 MPG. Repeating this calculation across three or four fill-ups and averaging the results gives you a reliable baseline figure. A single tank can be skewed by short trips, unusual weather, or an imprecise prior fill, so multiple measurements are more meaningful than any one data point.

Fuel Economy Calculator by Trip Distance

Once you know your MPG, this fuel economy calculator lets you estimate the cost of any trip. Enter your current fuel price per gallon alongside your trip distance, and the tool calculates the total fuel cost automatically. A vehicle getting 28 MPG on a 500-mile trip at $3.50 per gallon will use about 17.9 gallons and cost roughly $62.50 in fuel. The same trip in a vehicle getting 20 MPG uses 25 gallons and costs about $87.50. That $25 difference on a single trip adds up to hundreds of dollars over a year of regular highway driving.

Highway versus city mpg matters significantly here. EPA highway ratings typically run 20 to 30 percent higher than city ratings because highway driving involves less braking, fewer stops, and more consistent speeds. When estimating a mixed trip, using your combined EPA rating or your measured real-world number will give a more accurate cost estimate than relying on the highway figure alone.

Gas Mileage Calculator to Compare Vehicles

Comparing the fuel efficiency of two vehicles over a year of driving reveals the true cost difference between them. A vehicle getting 22 MPG driven 15,000 miles per year uses approximately 682 gallons. A vehicle getting 32 MPG on the same mileage uses about 469 gallons. At $3.50 per gallon, the more efficient vehicle saves roughly $745 per year in fuel alone. Over a five-year ownership period, that is $3,725 in savings before accounting for fuel price changes.

The liters per 100 kilometers figure is the metric equivalent used across Europe, Canada (for comparison purposes), and most of the world. It is inversely proportional to MPG: a lower L/100km number always means better fuel economy. The two figures are linked by the constant 235.215, so L/100km equals 235.215 divided by MPG. A vehicle rated at 30 MPG is equivalent to 7.84 L/100km.

Factors That Affect Your Real-World Gas Mileage

EPA ratings are measured under controlled laboratory conditions and consistently run higher than what most drivers achieve on the road. Several factors explain the gap between your rated and actual fuel efficiency.

• Driving style: aggressive acceleration and hard braking reduce MPG by 15 to 30 percent compared to smooth, gradual inputs
• Speed: aerodynamic drag increases sharply above 50 mph, and fuel economy typically drops 7 to 14 percent for every 10 mph above 50
• Cold weather: engines run richer when cold and electric accessories draw more power, reducing efficiency by 10 to 20 percent in winter
• Tire pressure: under-inflated tires increase rolling resistance and can reduce gas mileage by 0.2 percent for every 1 PSI below the recommended pressure
• Vehicle load: carrying extra weight in the trunk or towing a trailer reduces MPG proportionally
• Air conditioning: AC use can cut fuel economy by up to 25 percent in stop-and-go traffic

How to Improve Fuel Economy

• Use cruise control on the highway to maintain a steady speed and avoid fuel-wasting fluctuations
• Accelerate gently from stops and anticipate braking to avoid hard stops
• Keep tires inflated to the vehicle manufacturer's recommended PSI
• Remove cargo and roof racks when not in use to reduce weight and drag
• Service the engine at recommended intervals; worn spark plugs and dirty air filters reduce efficiency
• Combine short errands into single trips, as cold engine starts use significantly more fuel per mile