Regarding km/l or mpg, see https://what-if.xkcd.com/11/ which points out that the area term of the reciprocal - eg, liters per 100 kilometers - has a more direct physical interpretation:
> "If you took all the gas you burned on a trip and stretched it out into a thin tube along your route, 0.1 square millimeters would be the cross-sectional area of that tube [in a car which gets 20 MPG]"
> "If you took all the gas you burned on a trip and stretched it out into a thin tube along your route, 0.1 square millimeters would be the cross-sectional area of that tube [in a car which gets 20 MPG]"