The stadion (; ), formerly also anglicized as stade, was an ancient Greek unit of length, based on the length of a typical sports stadium of the time. According to Herodotus, one stadion was equal to 600 Greek feet (pous). However, the length of the foot varied in different parts of the Greek world, and the length of the stadion has been the subject of argument and hypothesis for hundreds of years. Various hypothetical equivalent lengths have been proposed, and some have been named. Among them are:

An empirical determination of the length of the stadion was made by Lev Vasilevich Firsov, who compared 81 distances given by Eratosthenes and Strabo with the straight-line distances measured by modern methods, and averaged the results. He obtained a result of about