Maybe you're in the middle of a hot job and can't wait for stock delivery. Maybe you only need a short piece of square stock and all you have is round stock, you would rather not have to buy a whole bar of square stock material. Whatever your reasoning is, here is a formula to help you choose the right size round stock if you need to make square material from it.
d = 1.414 x s
d = the diagonal from corner to corner
s = one side of the square you're trying to create
For example:
I want to create a piece of 1.25 square stock. What is the smallest round stock I can use to make this square and still get a sharp corner?
ANSWER: 1.7675 minimum diameter. If you don't mind a slightly rounded corner you could probably use 1.750 diameter.
No, if you only have round stock, you don't need to have square stock on hand. You can file, grind, or machine the round stock to make it into a square shape.