mileage, has at least 5 different definitions that I know of, however for the translation of the definition provided above, use, 'klicks' or 'kilometrage'. The later you can find in a french dictionary but not an english one, and is not widely used, likely because it is too had to say. The word, mileage, is still used in metric countries to denote distance and often people will respond 300k and make the assumption that you understood 300,000 km. The definition (variant) of the word very clearly means distance in miles and so the meaning has developed ambiguity in metric countries (because many metric countries converted from imperial to metric in the 70s), and an older person or a "smart ass" might assume miles. Thus to remove ambiguity, klick (or less favourably klik) should be used. You can find this word in both oxford and webster.

I speculate that the reason why there is no english word is because oxford (British) and webster (American) are the 2 prevailing authorities for the english language and neither of these countries use kilometres as their base unit of measurements. In Canada, the Quebec province explicitly has a linguistic department to create french words (in particular english equivalents), however there is not an linguistic department for english.