Measure gas mileage and fuel consumption
Record distance and fuel used between matching full-tank refills. Choose miles with US gallons, or kilometers with liters. Use actual fuel consumed for the same interval, not tank capacity. Cars, diesel trucks and 26-foot box trucks can use the same formulas with their own measurements.
The formula
Keep currency, units and time periods consistent. Percentage inputs use percentage points (enter 5 for 5%). Results are rounded only for display; tiny nonzero values may use scientific notation. Undefined ratios are shown as unavailable.
300 miles using 12 US gallons gives 25 MPG, about 9.41 L/100 km and 10.63 km/L.
MPG versus L/100 km
Higher MPG or km/L means the vehicle travels farther per unit of fuel. Lower L/100 km means it uses less fuel over a fixed distance. The conversion mode accepts any of these three units. US gallons are not Imperial gallons; this tool does not accept Imperial MPG.
Turn observed efficiency into a fuel budget
Use the measured MPG in Fuel Cost before a trip. Load, weather, idling and driving conditions can change consumption, so one refill is not a guarantee for the next trip. Fuel Consumption is consolidated here rather than repeated on another page.
Using this in a dispatch decision
Use measured fuel efficiency from consistent refills as an input to a trip budget, then allow for changes in load and driving conditions. This tool converts efficiency; it does not estimate a route or its price.
Method and reference sources
Method and content checked 2026-10-12. These sources provide background, not endorsement or professional certification. The formula and limitations above define this calculator.
- NIST — Unit conversion factorsUS liquid gallon, mile and fuel-efficiency conversion factors. Imperial MPG is not supported.
Frequently asked questions
Does this fuel consumption calculator use US or Imperial gallons?
US liquid gallons only. US MPG cannot be interchanged with Imperial MPG. For metric measurements, select kilometers and liters.
Can I convert L/100 km into MPG without refill measurements?
Yes. Select Convert fuel efficiency, choose L/100 km and enter the positive value. The result shows US MPG and km/L.
Why must distance and fuel both be greater than zero?
Zero fuel makes distance-per-fuel undefined. Zero distance makes fuel-per-distance undefined. Measure a traveled interval with positive fuel use.