How to use the fuel log analyzer
- Choose miles and gallons or kilometers and liters.
- The first row is your starting fill-up. Enter the odometer reading only. Its fuel amount is not needed, because that tank belongs to an earlier trip.
- For each later fill-up, enter the odometer, the fuel added and, if you like, the cost. Untick Filled to full for a partial fill.
- Read the economy for each stretch between full tanks, the overall average and the cost per distance.
Formula
stretch distance = odometer at its last full fill - odometer at its first full fill
stretch fuel = fuel added in every fill after the first one, up to and including the last
miles per gallon = distance / fuel (liters per 100 km = fuel / distance x 100)
Economy is reliable only between two full tanks, so partial fills are added into the stretch they belong to. The average uses total distance and total fuel.
Five fill-ups with one partial
The starting odometer is 48,200. The next full fill at 48,512 takes 10.4 gallons, a stretch of 312 miles at 30.0 mpg. At 48,790 a partial fill adds 9.1 gallons, and at 48,840 a full fill adds 1.6 gallons, so the stretch is 328 miles on 10.7 gallons, 30.65 mpg.
The last fill at 49,150 adds 10.8 gallons for 310 miles, 28.70 mpg. In all, 950 miles used 31.9 gallons, an average of 29.78 mpg. The three fills cost $38.90, $40.50 and $41.00, so the total is $120.40, or $0.13 per mile.
Why full tanks matter
Pumps shut off at slightly different points, and a partly filled tank hides how much was actually used. If you divide each fill by the distance since the last one, the numbers jump around. Using only full-to-full stretches, and adding partial fills into them, removes that noise.
Making the average useful
A longer log gives a steadier number. Compare the best and worst stretch with the average to see how much your economy varies with season, load and driving type. To plan a trip, use the MPG Calculator, the Fuel Cost Calculator and the Road Trip Fuel Stops Calculator.
Assumptions and limits
- Odometer readings rise from row to row.
- The first row is treated as a full tank.
- A stretch ends at the next fill marked as full. Fill-ups after the last full tank are left out.
- Costs are included only when every fill-up in a stretch has a cost.
Frequently asked questions
Why is the first fill-up's fuel not used?
That fuel filled the tank for the trip before your log began. Only the fuel added after it burns the distance you measured.
What if I forget to mark a fill as partial?
The page then treats it as full, which can make one stretch look better and the next look worse. The average over many stretches stays close, but the individual numbers will be off.
Can I use kilometers and liters?
Yes. Switch the units, and economy appears in liters per 100 km while cost is per kilometer.
What does a stretch with no cost show?
The cost per distance cell shows n/a for any stretch where a cost is missing, and the cost totals show a note until every fill-up has a cost.