The account at 1 Kings 7:26 refers to the sea as containing “two thousand bath measures” of water used by the priests, whereas the parallel account at 2 Chronicles 4:5 speaks of it as containing “three thousand bath measures.” This has led to the claim that the difference is the result of a scribal error in the Chronicles account.
However, the New World Translation helps us understand how these two texts can be harmonized. First Kings 7:26 reads: “Two thousand bath measures were what it would contain.” Notice that 2 Chronicles 4:5 says: “As a receptacle, three thousand bath measures were what it could contain.”
So 2 Chronicles 4:5 refers to the maximum capacity of the temple basin, what it could contain, whereas 1 Kings 7:26 states the quantity of water that was usually put into the temple basin. In other words, it was never filled to maximum capacity. It appears that it was customarily filled to only two thirds of its capacity.