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Record every fill the same way
For each fill, record the date, vehicle, driver, fuel station, litres, total cost and the odometer reading. Without the odometer reading, the fill can't be turned into consumption.
Fill to full where possible. Consumption is most accurate when you measure from one full tank to the next.
Litres per 100 km
Consumption (L/100 km) = litres filled ÷ kilometres driven since the last fill × 100.
Example: 120 litres after 500 km is 120 ÷ 500 × 100 = 24 L/100 km. Compare the figure with the same vehicle's past fills and with similar vehicles on similar routes.
Fuel cost per kilometre
Fuel cost per km = total fuel cost ÷ kilometres driven. Add your other running costs per km and you have the minimum price a trip must earn.
Use the unit converter if some of your figures are in miles or gallons — mixing units is a common source of wrong numbers.
Warning signs worth checking
A vehicle whose consumption jumps suddenly, fills where the odometer did not move since the last fill, fills larger than the tank can hold, and frequent small fills at unusual stations.
A sudden rise can be mechanical — tyres, injectors, air filters or a heavy foot — so check the vehicle before assuming anything else.
Ways to bring the cost down
Keep tyres at the right pressure, cut idling time, service vehicles on schedule, plan routes to avoid empty return trips, and compare drivers on the same route — the difference between the most and least efficient driver is often significant.