Check if a Square is Square

All you need to check if a square is square is a piece of plywood with a factory edge, a pencil and of course a square. You may be surprised by the results.


Use the factory edge of a piece of plywood or an edge that you know is perfectly straight to align the short side of your square. Draw a line along the edge of the long side of the square. Then flip the tool over, aligning the base of the mark with the same edge of the square; draw another line.

If the two marks don’t align, your square is not square.

When buying a square, it’s a good idea to check its accuracy before leaving the store. Bring a pencil and a long piece of paper or cardstock with you when you shop. Grab a handful of squares and head over to a sheet of plywood. Follow the steps above, marking the paper not the plywood, and then purchase the square the passes the test.

draw line down edge of square

draw another line down the edge of a square

check if a square is square