1 Kings 7:23, 26 - Now he made the sea of cast metal ten cubits from brim to brim, circular in form, and its height was five cubits, and thirty cubits in circumference … It was a hand-breadth thick, and its brim was made like the brim of a cup, as a lily blossom; it could hold two thousand baths.
Given the fact that the thickness of the cast sea is given, I would suggest that the circumference is the inner circumference and not the outer circumference.
1 cubit = 18 inches
10 cubits = 180 inches
30 cubits = 540 inches
1 hand-breadth = 4 inches
Inner circumference = 540 inches
Inner diameter = 180 – 4 – 4 = 172 inches
Circumference = Pi x Diameter
Pi = Circumference / Diameter
Pi = 540 / 172
Pi = 3.14
This is astounding given the fact that First Kings was written in the mid 500s BC. Actually, it's not astounding when one considers that the God who invented mathematics is the One who inspired the writing of First Kings.