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How to Use a Speed Square

Speed squares aren’t just for marking 90- and 45-degree angles when you’re cutting 2x4s. You can use a speed square to find roof pitches, guide your circular saw and more—including marking any angle from 0 to 90 degrees.

By the DIY experts of The Family Handyman Magazine

What is a speed square?

Ever wonder why every contractor you see has a triangular square stuck in his tool belt? This dandy little tool is often called a speed square, and it can offer you the biggest bang for the buck in your toolbox. I picked up the one shown in the photos for $3 at a home center in 1999. This tool has dozens of uses; here are three of our favorites.

How to use your speed square

With a torpedo level and a speed square, you can pretty accurately gauge the pitch of any roof with a gable end (Photo 1). The pitch tells you the amount of vertical rise (in inches) for every 12 in. of run. To find the pitch, just place the pivot point against the shingles. Then place a torpedo level on the fat base of the square and adjust the square until the level is level, and read the pitch on the side of the square.

You can use the speed square to mark an angle, such as when cutting a rafter tail, by holding the pivot point against the board. Swing the square until you read the desired angle on the board’s edge, and make your mark. Photo 2 shows how to use the speed square to mark a 33-1/2 degree angle—the same, as you would need on a rafter tail for a roof with an 8/12 pitch.

Before miter saws, and even since, professional carpenters used speed squares as a quick saw guide for cutting 45- and 90-degree angles. The plastic squares are thicker than most metal ones, making them a good fence for the shoe of a circular saw to ride along. This method works better (and safer) when right-handed users have a circular saw with the motor to the right of the blade (like the one in Photo 3).

Here are some other quirky uses we’ve heard speed squares put to: nail set, boot scraper, shim, butter knife and digging tool. It’s a good thing they don’t cost much.

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Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

    • Circular saw
    • Speed square

You’ll also need a torpedo level.

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

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