I agree with Dave.
Flaming hard to work out fuel consumption without keeping accurate records over many tanks.
For a single tank estimate, one has to develop the right technique in filling the tank. This usually involves using the same pump at the same servo, and stopping the fill on either the first or second click. One also needs to listen to the fuel in the filler tube to check that the tank is filled to roughly the same level at each fill.
Records spanning many tanks will average out the inevitable fill errors.
After all that, I am averaging around 11.4L/100 kms in Roo2 over my total mileage (2.5L N/A 5MT/DR 2006 XS).
On the open road, I tend to get between around 7.3-7.8L/100 Kms (on cruise control; two adults, with a bit of excess weight in the vehicle; aero roof bars, no baskets; tyre pressures 35 psi; Michelin XM2 tyres).
These figures are derived from the individual fill records over about 10,000 Kms that I record in my vehicle log book. I record Date, Mileage, Odometer (then reset), Litres, Cost, Place, Misc in the log book on one page; service & maintenance records on the facing page.
I have kept accurate log books for all our vehicles since around the mid 1980s.
