Most of us protestants do NOT see the Bible as a science book. The Bible was using language of appearance. In fact, the spot where PI is described, it is not percise. And the famous Christian Sciencist proof text does not say the earth is round even.
One of the most famous mathematical statements in the Bible is in I Kings 7:23-26, describing a large cauldron, or “molten sea” in the Temple of Solomon:
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. Below the rim, gourds encircled it - ten to a cubit. The gourds were cast in two rows in one piece with the Sea. The Sea stood on twelve bulls, three facing north, three facing west, three facing south and three facing east. The Sea rested on top of them, and their hindquarters were toward the center. It was a handbreadth in thickness, and its rim was like the rim of a cup, like a lily blossom. It held two thousand baths.
The passage saying the earth is round is Isaiah 40:22:
He sits enthroned above the circle of the earth, and its people are like grasshoppers. He stretches out the heavens like a canopy, and spreads them out like a tent to live in.
This passage may reasonably be interpreted as referring to a flat circular earth with the heavens forming a dome above it. Such an interpretation is consistent with other passages of the Bible which refer to a solid firmament (Gen. 1:6-20, 7:11; Ezekiel 1:22-26; Job 9:8, 22:14, etc.). It is also consistent with the cosmology common in neighboring cultures.
Isaiah 11:12 refers to the “four quarters of the earth”, but we do not take that as indicative of the earth’s shape.
The shape of the earth may already have been known in Isaiah’s time. Ancient astronomers could determine that the earth was round by observing its circular shadow move across the moon during lunar eclipses. There is some suggestion that the Egyptians knew of the earth’s spherical size and shape around 2550 B.C.E. (more than a thousand years before Moses). The Greek philosopher Pythagoras, who was born in 532 B.C.E., defended the spherical theory on the basis of observations he had made of the shape of the sun and moon (Uotila 1984). If this information was known by educated Greeks and Egyptians during biblical times, its use by Isaiah is nothing special.