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How to Use a Speed Square

“There’s so much math that this takes care of for you, where you don’t have to figure it out with a calculator. Look at all of the features that a speed square has to offer, and then learn how to use them—that’s the biggest thing that I can recommend. -Jordan Smith

A speed square is a simple, inexpensive, and lightweight hand tool essential for doing construction math. Beyond math, it has a multitude of uses on any job site. You can use it to determine a roof pitch, mark angles, guide saw cuts, scribe straight lines, and check if something is square. It’s also made of a singular piece of metal or plastic so that if it hits the ground while you’re working, it will still remain true.

What is a speed square?

Despite the word “square” in the name, a speed square is actually a right triangle with a perfectly 90 degree (square) edge and two 45 degree corners. It can also be referred to as a rafter square, triangle square, steel square, carpenter square, or framing square. 

The name speed square comes from the tool’s main purpose—to speedily measure whether something is square—meaning, that the angle is exactly 90 degrees. It looks a lot like a heavy duty version of your protractor from geometry class combining a protractor, ruler, saw guide, square checker, common-width board ripping guide, and line scribing tool all in one.

Common uses of a speed square on a construction site

While a speed square has many uses, these are the most common applications you’ll use job after job:

  • Determining roof pitch: Combined with a spirit level, the internal markings on a speed square can determine the pitch of a roof by placing the pivot point at the shingles and the level on the flange surface. Then adjust the square until level and read the angle to learn the pitch or vertical rise measurement for every 12 inches of run (the horizontal measurement).
  • Guiding saw cuts: The flanged bottom of the speed square hooks onto the edge of your lumber and held tightly with your hand, the side of the speed square acts as a guide for a circular or other power saw to cut straight across (at a 90 degree angle). Flip the speed square to make the same cut but at a 45 degree angle.
  • Measuring and checking angles: The flanged bottom of the speed square hooks onto the edge of your lumber and measures or checks 45 and 90 degree angles. You can also measure any angle from 0 to 90 degrees using the pivot point. 
  • Scribing straight lines: Much like the speed square acts as a guide for a saw, it can act as a ruler to help you scribe accurate straight lines at 90 and 45 degree angles.


Get a complete tutorial on how to use a speed square like a pro from builder and craftsman Jordan Smith in MT Copeland’s Hand Tools online course.

How to use a speed square to measure an angle on lumber 

In addition to measuring roof pitch, measuring angles on lumber is something you will do all the time on a construction site, especially if you are in carpentry. There are many markings on a speed square to help you measure angles quickly and accurately so make sure you learn how to read each marking on your speed square to get the most out of your tool.

Step 1: Align the flange

Align the flange on the bottom of the speed square with the edge of the lumber and hold it securely in place. At this point you can draw a line across the bottom edge to mark a 90 degree line (straight cross cut), or flip the speed square to draw a 45 degree cut line.

Step 2: Locate the pivot point

To measure any angle between 0 and 90 degrees, locate the pivot point in the bottom corner of the speed square where the flanged edge meets the straight edge. Securing the speed square at the pivot point, slide it so that the edge of the lumber is at the desired angle. Angle measurements are on the diagonal side of the tool.

Step 3: Scribe the cut line

While firmly holding the speed square in place, use the edge to scribe the cut line. Repeat this process with any desired angle up to 90 degrees.

MT Copeland offers video-based online classes that give you a foundation in construction fundamentals with real-world applications. Classes include professionally produced videos taught by practicing craftspeople, and supplementary downloads like quizzes, blueprints, and other materials to help you master the skills.

Avatar Photo of Jordan Smith

Featured Instructor

Jordan Smith

Jordan Smith is the CEO and Founder of Smith House Company, a design+build firm based in Austin, Texas. He learned to build and weld while working on the farm with his grandad, and after earning a degree in Welding and Materials Engineering, he spent the next 10 years working in the heavy construction building everything from robots to ships to offshore oil rigs before transitioning to residential construction. After spending a couple of years working with industry leading builders in Austin, Jordan and his wife Veronica struck out on their own to form Smith House Co. Smith House Co. strives to build more beautiful, functional and resilient spaces which are self sustaining and harmonize with their natural surroundings.

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