1 Kings 7:23 (RSV)

also in

2 Chronicles 4:2

Then he made the molten sea; it was round,
ten cubits from brim to brim,
and five cubits high,
and a line of thirty cubits measured its circumference.

Since pi is the ratio of the circumference to the diameter (30:10),
pi equals 3
It's in The Book! No need to memorize 3.14159265358979...