How To Use A Speed Square - The Family Handyman

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A Step by Step Guide for How to Use a Speed Square

By Family Handyman

Family Handyman's Editorial Process

Updated on Sep. 01, 2025

Get the most out of this handy little triangle

Introduction

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.

What is a Speed Square?

Ever wonder why every contractor you see has a triangular square stuck in his tool belt? This cheap, handy little tool is called either a rafter square or a speed square, and it can offer you the biggest bang for the buck in your toolbox. This tool has dozens of uses; here are three of our favorites.

Tools Required

• Circular saw
• Speed square

Project step-by-step (3)

Step 1

Find Roof Pitch

• Place the pivot point against the shingles.
• Then place a torpedo level on the fat base of the speed square.
• Adjust the square until the level is level.
• Read the pitch on the side of the speed square.
  • Note: The pitch tells you the amount of vertical rise (in inches) for every 12 inches of run. 

Step 2

Mark Angles

• Swing the speed square until you read the desired angle on the board’s edge.
• Mark the angle on the board.
  • Note: The example shows a 33-1/2 degree angle.

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Complete DIY projects like a pro! Sign up for our newsletter! Do It Right, Do It Yourself! Step 3

Guide Saw Cuts

• Cut 45- and 90-degree angles by using the speed square as a guide.
  • Pro tip: This method works better (and safer) when right-handed users have a circular saw with the motor to the right of the blade (like in the photo).