This article is from the Atheism FAQ, by mathew email@example.com with numerous contributions by others.
In I Kings 7:23, the Bible says:
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.
If you make a molten sea with a circumference of thirty cubits, you'll
find that the diameter is 30/pi or 9.55 cubits. Or ten cubits, to
round to the nearest integer.
In short, the Bible does not say that pi must be three, unless you are
going to assume that the numbers given are accurate to more than two
significant figures, which is unjustifiable given the wording.