Published 2026-09-26
A pump-side habit that makes economy and fuel cost readable.
Mileage here means the odometer, and the distance between fill-ups. It does not mean a guess from the trip computer after one commute.
Track fuel if you want to know what the car drinks. Track it with the odometer if you also want liters per 100 km or miles per gallon.
01
Write the kilometers or miles at the pump. Doing it later from memory is how logs go wrong.
02
Volume and cost, from the receipt. Use the same units every time. Mixing liters and gallons in one log will not average itself into the truth.
03
You do not need a full tank for the row to count. You need honesty about how much you bought. Economy is clearer when most fill-ups are to full, because the tank starts from a known point.
04
If you skipped three weeks, leave them skipped. One perfect tank does not describe a month you did not record.
The fuel economy tool on this site divides one distance by one amount of fuel. That is enough for a trip or a tank. It forgets the result when you close the page.
A log is the same division repeated. Winter, a roof box, or a new commute show up because the rows are still there. RPMBase keeps those rows on the car.
Sometimes you only need the odometer: before a long trip, after one, or when a service asks for it. That is a mileage reading, not a fuel row. Keep it separate so it does not look like a purchase.
Every fill-up you want included. Occasional logging is fine for cost. It is a weak way to judge economy.
Trust a stretch of recorded fill-ups more than one tank, and more than the trip computer after a reset. The owner's manual figure is a lab number, not your roads.
