Wind Waker Great Sea size?

I have tried to calculate the size of the Great Sea in Wind Waker, and came up with a value of 144 sq. miles. The only problem is that the same calculations resulted in the full speed of Link's boat to be several thousand miles per hour. The Sea Chart in the game gives a size for the Great Sea (7000x7000), but the units are in Hylian and the actual characters are too small to be even translated into Japanese. What do you think the measurement units are?