1 Kings 7:23-24
He made the Sea of cast metal, circular in shape, measuring ten cubits from rim to rim and five cubits high. It took a line of thirty cubits to measure around it.
I read about this years ago in a book on pi. While I would joke with people about this "proving the Bible wrong" to get a reaction, I think there's plenty of room for a plausible explaination.
The verse seems to speak of the width around (circumference) being measured. It talks about a "line of 30 cubits" being used to measure it around. I would assume this is the starting point. This is what was measured. Whether the diameter (from rim to rim) was actually measured r merely calculated is uncertain. To start with diameter and multiply would then give you a false conclusion, especially when rounding is no-doubt involved.
As stated, 30/pi = 9.549, which rounds up to 10. I don't recall seeing decimal points being used in the Bible, so numbers would probably be rounded off.
While 9.549 rounds up to 10, it's real close to the half-way point between 9 and 10. Let's say the object was a little larger than 30 in circumference. Let's say 30 1/3, that makes the diameter 9.655 (about 9 2/3). 30 1/3 could easily be rounded down to 30 and 9 2/3 is now a lot closer to 10 and could easily be rounded up.
Did the ancients even round up or down the way we do? That is, .5 or above, round up and below .5, round down? Or was everything above a whole number rounded up? Or down?
Was the object really a perfect circle? If slightly oval, it could appear circular, but actually measure slightly smaller across at some points than others. We are talking about what? Approx. 15 feet across. That's a large circle. Although I could be biased and view all ancient civilizations as primitive, I'm not sure they had the means to make a perfect circular bowl (or whatever a "sea" is) of that size. I would think it's very possible it came out somewhat oval.
While I do believe that the Bible has its inconsistencies, I think this is far from a smoking gun.