A right angle is the standard by which all carpenters build. When corners meet at 90 degrees, drawers fit snugly, windows close tight, and walls stand straight. The key to all this is a square. Most provide a fixed 90-degree angle in various forms, and some can help copy or draw other angles.
"The first square you buy should be a 12-inch speed square," says Tom Silva, This Old House general contractor. "It's versatile and unbreakable. It gives you 45- and 90-degree angles, it's also a ruler, and it's not hard to measure other angles with it, too."
Tom grew up using a traditional L-shaped framing square, which he still prefers for laying out a pattern rafter or a stair stringer. And anytime he's working in the shop, he keeps a combination square, with its sliding head, close at hand for gauging lines. On the job, though, Tom does most routine carpentry with a couple of speed squares. "I use the 12-inch one as a crosscut fence for my saw and router, and the 6-inch one is always in my apron pocket—it's especially handy when I'm up on a ladder."
You'll find many types of squares on the shelf at the home center, but you don't need them all. Use the basic models we show here whenever you measure and cut; add specialty squares, such as a drywall square or a sliding T-bevel, as your current projects require.