- US fuel economy
- 30 mpg
- Consumption
- 7.84 L/100 km
How it works
Combine fuel before averaging mileage
Two 300-mile intervals using 10 and 15 gallons produce 24 mpg overall: 600 ÷ 25. Averaging the separate 30 and 20 mpg figures gives 25 mpg and overstates economy. Sum distance and fuel first.
Calculating fuel economy from a measured trip
Use the distance traveled and the fuel consumed over the same interval. Odometer mode helps derive distance from two readings, but the fuel measurement still needs to match that journey. Distinguish miles per gallon from liters per distance when comparing results. A single trip's economy can differ from a longer-term average because conditions and measurement error vary.
US fuel economy: formula and assumptions
US mpg = miles/US gallons; L/100 km = 235.214583/mpg.
Measure fuel over several fill-ups for a more stable estimate.
Metric consumption: formula and assumptions
L/100 km = liters/km×100.
The tank should be filled consistently at the start and end.
Odometer and fuel cost: formula and assumptions
Distance=end−start; mpg=distance/fuel; cost per mile=fuel×price/distance.
Use consistent full-tank measurements. End odometer must exceed the start.
Worked example
Using the US fuel economy example:
- Distance traveled (miles)
- 300
- Fuel used (US gallons)
- 10
US mpg = miles/US gallons; L/100 km = 235.214583/mpg.
Example result
US fuel economy: 30 mpg
Consumption: 7.84 L/100 km
These are illustrative inputs. Change the values to explore a different scenario.
Formula references
References explain the underlying methods; they do not imply endorsement or individual professional review of Finflo.
Common questions
How can inconsistent fill-ups distort mileage?
Fuel added is a useful estimate of fuel used only when the tank starts and ends at a comparable fill level.
Why do lower L/100 km and higher mpg both indicate better economy?
L/100 km measures fuel used for a distance, while mpg measures distance traveled per unit of fuel. Their directions are opposite.
Prepared by Finflo. See our methodology and editorial policy.