[saltedshiv]

But could you change it to km-per-litre?

[bonoboTP]

Litre-per-100km is the European standard.

[tzs]

Dimensionally, that has units of area, and so could be expressed in hectares. My car is getting about 11.5 pico hectares.

[bonoboTP]

The same way that torque has the dimensionality of energy and can be measured in joules.