Keep a complete refuelling record
- Fill according to your vehicle’s instructions, with the engine off. Use a consistent filling method; do not overfill. Record the date and odometer in kilometres.
- Keep every receipt and record litres and the amount paid. Mark a fill as full only when it really is. A partial fill is included once the next full fill closes the interval.
- If a purchase is missing, start a new reliable interval from a full fill. Do not infer missing litres from the fuel gauge or the tank’s nominal capacity.
Example: a partial fill between two full tanks
Illustrative records: full at 50,000 km; 20 L added without filling up at 50,300 km; 29 L to full at 50,700 km. The interval covers 700 km and 49 L, giving 7 L/100 km. These are invented example values, not a benchmark for your car.
Calculate fuel purchases per kilometre
Suppose the two later purchases cost €36 and €52.20. Their €88.20 total divided by 700 km is €0.126/km, displayed rounded as €0.13/km. These prices are illustrative. This is fuel purchasing cost for the interval, not total ownership cost; it excludes servicing, insurance and electricity.
Compare like with like
Repeat over several full-tank intervals. For an overall average, divide total litres by total distance, rather than averaging individual L/100 km figures. Traffic, weather and driving conditions affect the result. A higher value alone does not diagnose a fault. Monthly purchases also differ from monthly consumption because fuel remains in the tank.
Keep each vehicle separate in Energy Detective
In My places & vehicles, add or select a Vehicle. Open Fuel log → Add fuel purchase and enter date, odometer, litres and amount paid; set Filled to full correctly. You can attach a receipt photo and note. The app includes partial fills between full ones and shows L/100 km and fuel cost/km. It calculates from your records, not from a live vehicle sensor.
