How to calculate fuel consumption in L/100 km

The calculation, with a simple example

Suppose you fill the tank, drive 500 kilometres and then need 45 litres to fill it again. The calculation is 45 ÷ 500 × 100 = 9.0 L/100 km. Under that measurement method, the second fill replaces the fuel used during the distance between the two full-tank readings.

Lower L/100 km means less fuel used over the same distance. Keep the unit in mind when comparing figures: litres per 100 kilometres and miles per gallon run in opposite directions. A larger miles-per-gallon number describes more distance per unit of fuel; a larger L/100 km number describes more fuel for the same distance.

Do not divide the fuel bought today by the vehicle’s entire odometer reading. You need the distance for the same interval as the fuel. Subtract the starting odometer from the ending odometer and check that both readings belong to the same vehicle.

Why full-to-full records matter

A full starting tank gives you a repeatable reference point. The next suitable full fill closes the interval. This is why your first full-tank entry usually establishes a starting point rather than immediately producing a reliable consumption figure.

If you add fuel partway through that interval, keep the partial fill in your records. Imagine adding 20 litres, driving farther and then adding another 25 litres to reach full again. The total fuel for the interval is 45 litres, not just the 25 litres on the final receipt. Pair that total with the distance since the previous full tank.

Missing a fill can make the result look unusually efficient. Incorrect odometer readings can distort it in either direction. When a number seems implausible, inspect the records before deciding the vehicle’s performance changed.

Record a fill-up in DriveFive

1. Choose Fueling or Add fuel on Home, then confirm the vehicle, date and dashboard odometer.
2. Enter the litres and mark honestly whether the tank was filled completely.
3. Enter the total paid or the pump price when you know it. If the cost is unknown, leave the price fields blank rather than inventing an amount.
4. Add a station, receipt or note under More details & receipts if useful, then save.
5. If a fill was missed, use the missed-fill option so the incomplete interval is not treated as reliable consumption data.

DriveFive uses suitable full-to-full intervals and includes partial fills between them. Missing costs do not stop known litres from contributing to fuel-consumption records. They do affect cost-based results, which need the money side of the record as well.

Fuel economy and fuel cost answer different questions

The same 45 litres might cost different amounts at different pumps or on different days. The vehicle could use the same fuel over the same distance while your receipt gets larger. That is a price change, not automatically a fuel-economy change.

For example, a hypothetical $76.50 spent over a complete 500-kilometre fuel interval works out to $0.153 per kilometre in fuel cost. That calculation does not include maintenance, insurance, financing or other ownership expenses. Label the result clearly so you do not mistake fuel cost for the vehicle’s total cost.

Compare records using the same vehicle and a sensible date range. A single unusual interval deserves inspection; several complete intervals give you more context. Check the underlying entries and note changes in how the vehicle was used before drawing conclusions.

A quick check when the number looks wrong

• Look for a misplaced digit in either odometer reading.
• Confirm the litres belong to this vehicle and this fill-up.
• Check whether a partial fill was accidentally marked as full.
• Look for a missing fuel purchase between the two full readings.
• Separate missing price information from missing fuel-volume information.

Keep the record truthful even when that means leaving a result unavailable for now. A blank value tells you something is missing. A plausible-looking number built from incomplete entries is harder to spot later. Once the records are corrected, review the interval again and export the fuel report if you need a copy.