How To: Determine If Your Carpenter’s Square Is True

A square is worthless if it isn't actually square. Learn this quick, simple way to make sure your square is just that.

Carpenters Square

To determine whether a carpenter’s square is true, all you need is a straight line. Sound too simple?

First you lay the square to be tested flat, its blade tight to the line. Then draw a second line along the tongue.

Now flip the blade over, and snug the heel to the square into the (supposedly) ninety-degree angle next to the one you’ve just drawn. Draw a third line.

It the square is true, lines two and three should be the same and are, therefore, perpendicular to the first: Your square is indeed square.

If not…Well, that tool is no fair square.