Fuel consumption: what does it mean?

From fuel receipt to consumption

Start with a full tank and note the odometer. When you fill up again, record litres added and distance driven. Divide litres by distance and multiply by 100.

If you topped up in between, count those litres when you next fill up completely. A partial receipt does not tell you how much you used since the last stop. Totals across several complete intervals give a steadier picture.

Compare similar journeys where possible. Short trips, speed, load and weather can affect consumption. Check the test method when comparing with an official figure.

42 litres for 630 kilometres

You refill 42 litres after 630 kilometres. That is 42 ÷ 630 × 100 = 6.7 l/100 km, or 630 ÷ 42 = 15 km per litre. Keep the unit consistent when comparing results.

Compare several full-tank intervals before drawing conclusions from one unusual reading.

Choosing a period with complete fuel records

A fuel receipt shows how much you bought at that stop. To compare consumption, you also need distance and a consistent level at the start and end. Combining consecutive fills reduces the effect of a pump nozzle cutting off a little early.

Write down litres and the odometer reading at the pump. Flag any missing fill. Otherwise consumption can look artificially low because some of the purchased fuel is missing.

A partial fill still counts towards the litres you bought. End the calculation at the next comparable full tank. That saves you from estimating how much fuel was in the tank during the intermediate stop, when you may only have added a small amount.

Calculating a reliable average

The odometer shows 70,000 km at the first full tank. At the next full tank it reads 70,600 km and you add 39 litres. Divide 39 by 600 and multiply by 100. The result is 6.5 litres per 100 km.

Compare similar winter months to see whether a pattern has changed. Journey length, traffic, speed and load may vary considerably.

For several fills, add all the litres and distances before dividing total litres by total distance. An ordinary average of separate consumption figures gives a short interval the same weight as a much longer one. Use the totals when you want a figure for the whole period.

If consumption keeps climbing on similar trips, identify what has changed. Check the tyres as directed in the handbook and tell the workshop about any unusual increase alongside warning messages.

Recording litres and fuel costs

Keep the price of each fill if you want to calculate trip costs later. Store litres and money as separate figures.

Keep any receipt without an odometer reading. If you have the start and end readings for the complete series, you can include those litres in the total without inventing a reading for the individual fill. Mark the missing field in your records.

When switching between litres per 100 kilometres and kilometres per litre, label the units beside every result. A smaller figure means lower consumption only in the first format.