Gas Mileage Calculator

A gas mileage calculator turns the distance driven and the fuel consumed into a fuel efficiency figure, miles per gallon (MPG), kilometers per liter (km/L), or liters per 100 kilometers (L/100km), depending on the units used. An optional fuel price adds a cost-per-distance-unit breakdown and a total fuel cost for the trip.

• Distance driven accepts whole numbers, decimals, fractions (3/4), and mixed numbers (175 1/2), in either miles or kilometers.
• Fuel used accepts fractions or decimals, in gallons or liters, so a partial fill-up can be entered exactly as pumped.
• An optional fuel price per unit adds the cost breakdown; dollar signs and commas are stripped automatically.
• Settings can show the step-by-step substitution and arithmetic behind each result, and can add the metric L/100km figure alongside the primary efficiency result.
• The formula for miles per gallon is: MPG = Distance / Fuel Used. For kilometers per liter: km/L = Distance / Fuel Used. For liters per 100 km: L/100km = (Fuel Used / Distance) x 100.

A 250-mile trip that used 10 gallons of fuel computes to 250 / 10 = 25 MPG. At $3.00 a gallon, total fuel cost is 10 x 3.00 = $30.00, or 30.00 / 250 = $0.12 per mile.

Fuel efficiency tracking serves drivers, fleet managers, and travelers who need accurate per-trip or per-vehicle consumption data. Below are scenarios where the results provide direct value.

• Daily commuting: Record odometer readings and fuel fill-ups each week to monitor whether driving habits, tire pressure changes, or seasonal fuel blends affect MPG over time.
• Road trip planning: Enter a planned route distance and the vehicle's known fuel consumption rate to estimate total gallons or liters needed and the expected fuel cost before departure.
• Fleet management: Compare fuel efficiency across multiple vehicles in a commercial fleet by logging distance and fuel for each truck or van after every refueling stop.
• Vehicle comparison: Test two vehicles over identical routes and compare the resulting MPG or km/L figures to inform a purchase or lease decision with real-world data rather than manufacturer estimates.
• Maintenance diagnostics: A sudden drop in fuel efficiency often signals mechanical issues such as clogged air filters, underinflated tires, or failing oxygen sensors. Tracking MPG trip by trip highlights these changes early.
• Rental car evaluation: Log the distance driven and fuel purchased during a rental period to verify the actual efficiency against the rental agency's stated fuel economy class. Compare results across multiple rental trips to identify which vehicle categories deliver the most value.
• Budget forecasting: Multiply the cost per mile or cost per kilometer by projected monthly driving distance to estimate the fuel line item in a household or business budget. Adjust the fuel price input to model different price scenarios and plan for seasonal fluctuations in fuel costs.
• Driving habit optimization: Record mileage before and after adopting fuel-saving techniques such as steady cruising speeds, reduced idling, or lighter cargo loads. Quantify the improvement in MPG or km/L to validate which habits produce measurable savings at the pump.
• Hybrid and electric comparison: Enter fuel consumption data from a conventional vehicle alongside equivalent trips in a hybrid to produce side-by-side efficiency figures. Pair the cost-per-mile output with electricity rate data to build a complete operating cost comparison between powertrains.