Sorta. The stade was based on the pous which varied. But not that much, and in ways that are often consistently documented. Around the time Eratosthenes was alive, give or take a couple hundred years, it was documented that 1 Roman mile = 8 stades, which gives us something to go of off. While there are other possible definitions, we do have one that we know is probably closest to whatever Eratosthenes used.

EDIT - the numbers regarding the error range in this source is likely inaccurate, but goes into the units issue

https://maa.org/press/periodicals/convergence/eratosthenes-and-the-mystery-of-the-stades-how-long-is-a-stade