How to Use a Speed Square

Updated: Apr. 03, 2023

Get the most out of this handy little triangle

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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.

Tools Required

  • Circular saw
  • Speed square

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.

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.

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).