The Pethagorean theorem is not mentioned. The Gemara uses 1 and 2/5 which only works for a square, as Tosafos points out, and is not exact.
Without decimals Chazal could easily have said to measure 3 and a seventh, or Shlosha Ushviis, or at least Shalosh Umashehu as we do by the Techum. They could also have mentioned Ve’od.