Among Temple fixtures is a “molten sea,” a metal, fountain-type structure (1 Kings 7). It is described as 10 cubits across and 30 cubits “to compass it round about.”
The Babylonia Talmud uses this text to argue a general conclusion that circumference is three times dimeter (Eruvin 14a). This has long been discussed as an inexact approximation of pi.
Steven Dutch, a natural and applied sciences professor at the University of Wisconsin-Green Bay, explores this concept in some depth. See “Pi in the Bible?”