Fuel consumption in Germany is usually measured in l/100 km.
Now l = dm³ (according to at least one definition), so that reduces to 0.01 mm²...
Though "My car gets 0.07 mm²!" will probably get a response along the lines of "What you say?" ^^
(Or you could claim 0.017 nanoacre instead of 0.07 mm² if you prefer imperial measurement. And the metric equivalent of mpg [which is range, not consumption rate] would be 1/mm², perhaps? 1 mpg = 1/(2.35 mm²) or 0.43 mm-2.)