> And he made a molten sea, ten cubits from the one brim to the other: it was round all about, and his height was five cubits: and a line of thirty cubits did compass it round about.
1 Kings 7:23 King James
In the original Hebrew version of I Kings, in that verse the word for 'circumference' is traditionally written differently to how it is read (there are instances of this kind of thing all over the Bible [1])
Each letter in Hebrew has a numeric value [2].
As written: קוה = 111
As read: קו = 106
Ratio between them: 111/106 = 1.04717...
Which is exactly the ratio between the reported value of pi (3) and the real value to 4 decimal places (3.1415)
So maybe they did have a better idea than "3". The 3 in the verse is to keep it simple, but there's a clue there for those who want the real number.
How many significant figures was it to? How accurate was construction and measuring techniques? 9.7 diameter would be reasonable as “10”, as would 30.47 being “30”, with values being well within 5%.