Use this free Gas Mileage Calculator to calculate MPG, kilometers per liter and liters per 100 kilometers from distance traveled and fuel used. Compare fuel economy and estimate driving range or fuel cost.
How the Gas Mileage Calculator works
The Gas Mileage Calculator measures how far a vehicle travels for each unit of fuel. It converts the entered distance and fuel volume into US miles per gallon, kilometers per liter and liters per 100 kilometers. These formats describe the same fuel economy from different perspectives.
MPG and km/L are distance-per-fuel measures, so a higher result means better efficiency. L/100 km is a fuel-per-distance measure, so a lower number means better efficiency. The calculator displays all three to make international vehicle comparisons easier.
Gas mileage formulas
Miles per gallon
MPG = miles traveled ÷ US gallons used. A vehicle traveling 360 miles on 12 US gallons averages 30 MPG.
Kilometers per liter
km/L = kilometers traveled ÷ liters used. If a vehicle covers 600 kilometers using 50 liters, the result is 12 km/L.
Liters per 100 kilometers
L/100 km = liters used ÷ kilometers traveled × 100. With 50 liters over 600 kilometers, consumption is approximately 8.33 L/100 km.
The calculator distinguishes US gallons from Imperial gallons. One US gallon equals approximately 3.785 liters, while one Imperial gallon equals approximately 4.546 liters. Selecting the wrong gallon type can materially change the result.
Accurate fill-up method
Begin with a full tank, reset the trip odometer or record the main odometer, and drive normally. At the next fuel stop, refill the tank to a similar level and record both the distance traveled and the fuel added. The refill amount approximates fuel consumed during that interval.
One tank may be affected by pump shutoff differences, short trips, unusual traffic or weather. Combining several tanks produces a more stable estimate. Add all distance values together, add all fuel values together, and enter the totals.
Worked example
A driver travels 360 miles and uses 12 US gallons. The Gas Mileage Calculator divides 360 by 12 to obtain 30 MPG. This is about 12.75 km/L or 7.84 L/100 km. At $3.50 per gallon, the fuel used costs $42.
Why actual gas mileage changes
Fuel economy varies with vehicle condition and the way it is used. Stop-and-go traffic, short cold trips, high speeds, rapid acceleration, heavy cargo, roof racks, towing, strong wind, steep terrain, low tire pressure and extensive idling can increase fuel consumption. Moderate speed, smooth acceleration and correct tire pressure generally support better efficiency.
Seasonal fuel blends and temperature may also influence results. Compare similar routes and conditions rather than assuming one tank represents long-term vehicle performance.
MPG versus advertised ratings
Official ratings are standardized estimates that help shoppers compare vehicles. Your result is based on actual distance and fuel entries. A difference does not automatically indicate a mechanical problem, because the official test and everyday conditions may not match. A sudden, sustained decline can justify checking tire pressure, maintenance, route changes and driving conditions.
Using fuel economy to estimate range
Estimated range equals usable fuel capacity multiplied by MPG or km/L. Leave a practical reserve rather than planning to consume every unit of fuel. Route availability, weather, traffic and elevation should be considered on long journeys.
The Gas Mileage Calculator provides a transparent estimate from your own fill-up records. For official fuel-economy data and vehicle comparisons, consult FuelEconomy.gov. Enter totals from several tanks when possible. The Gas Mileage Calculator becomes more representative when unusual trips do not dominate the sample.
Frequently asked questions about the Gas Mileage Calculator
What is good gas mileage?
There is no universal threshold. Vehicle size, engine type, road conditions and intended use matter. Compare the vehicle with similar models and track changes in its own historical average.
Should I use the fuel added or tank capacity?
Use the amount added at the end of the measured driving interval. Full tank capacity does not show how much fuel was actually consumed.
Can I calculate mileage with kilometers and liters?
Yes. Select kilometers and liters. The result includes km/L, L/100 km and an automatically converted US MPG value.
Why are US and Imperial MPG different?
The gallon volumes differ. An Imperial gallon is larger, so the numerical Imperial MPG for the same vehicle would be higher than US MPG.
Does the calculator store my driving data?
No. Calculations run in your browser. Download or record the result if you want to keep it.
Gas Mileage Calculator Example
If a vehicle travels 360 miles using 12 gallons, fuel economy is 30 MPG. Enter the same distance and fuel units used by your receipts or trip meter, then compare several full-tank intervals rather than relying on one short trip. Weather, traffic, tire pressure, payload, speed, and idling can all change the observed result.
How to Improve Gas Mileage Calculator Accuracy
For the most reliable Gas Mileage Calculator result, reset the trip meter after filling the tank, drive normally, and record the fuel needed at the next full refill. Repeat this over several tanks and compare the average with the vehicle information available from FuelEconomy.gov. Short trips and partial fills can produce misleading MPG estimates.