How to Use a Speed Square

Speed square measuring wooden beams

The Spruce / Margot Cavin

In This Article

At first glance, a Speed Square may look like an innocuous metal triangle more suited for art projects than for home projects. But this inexpensive tool can be your most powerful ally in many home remodeling projects. Because a Speed Square packs so many features into such a small tool, it can often be difficult to understand. Numbers are squeezed together, and there are cryptic lines, hash marks, and holes. Learn how to decipher a Speed Square's markings and use the tool properly.

What Is a Speed Square?

Nearly a century old, Speed Square is a renowned measuring tool patented and trademarked by the Swanson Company, which still manufactures the tool from its Frankfort, Illinois headquarters. Also known as a rafter square or triangle square, the Speed Square is a multi-purpose tool for carpenters and can be used to measure lumber and saw cuts, among many other things. Much like Kleenex, Speed Square is the most common name for this type of tool, even though Stanley, Irwin, DeWalt, Empire, and a host of other tool companies produce similar products under alternate titles. 

How to Use a Speed Square

How can a single piece of heavy-gauge aluminum with no moving parts attract so many fervent fans? A Speed Square's true secret lies in the dense congregation of information and features packed on its face: a lipped fence, deeply incised numbers, holes, notches, and cut-outs.

It's these features that make this a highly functional yet very low-cost tool for scribing, marking, and cutting. The accompanying 59-page "Swanson's Little Blue Book" is legendary in fine carpentry and roofing trades for helping to translate the Speed Square measurements to real-world applications.

  1. Understand the Variety of Uses

    A Speed Square covers a surprising array of uses. Understanding the basics of what it can do is the first step to using it for a wide variety of home improvement projects. Here are a few of those options:

    Use as a Saw Guide: Lip the Speed Square fence over the side of the board and cut against the square with a power saw.

    Square a Power Saw Blade: Unplug the saw and rest the square against the side of the blade to adjust the blade to 90 degrees.

    Find the Width of a 2x4: The diamond-shaped hole is 3 1/2 inches from the end—the true width of 2x4s.

    Measure Between 0 and 6 Inches: Hook the lip of the square over the board. The numbers above the "Swanson Speed Square" insignia will produce the measurement.

  2. Learn the Markings and Features

    Understanding what the markings and features mean can help you use the Speed Square.

    T-Shaped End: Hang this t-shaped end over the side of a board. Or use it as a stand for letting the Speed Square stand up by itself.

    Numbers 1-6 on the Side: These are inch marks and inch numbers. Note that a Speed Square actually measures up to 7 inches, not 6 inches. The 7th inch is the very end of the tool and is unmarked.

    Diamond-Shaped Hole: This hole is 3 1/2 inches from the end. It is a helpful quick measurement since the width of 2x4s is actually 3 1/2 inches, not 4 inches.

    Numbers 5-80 on the Long Side: These are angle degree numbers, not inch marks and numbers. Degrees between 0 and 5 are not marked with numbers, nor are degrees above 80 degrees.

  3. Use a Speed Square to Cut Trim at an Angle

    Let's say you want to cut two pieces of flat trim or any material each at 45-degree angles. You want to form a 90-degree angle with those pieces. You may need to form angles like this when installing door or window trim, and this can be done with a Speed Square.

    You can always haul out your electric miter saw or hunt for the manual miter box, but with the Speed Square, you can lay the square against the trim and create quick 45-degree pencil marks with the square. Do not cut directly against the square. Instead, remove the square and cut by following the line.

  4. Use a Speed Square to Find a Level

    Use the Speed Square as an improvised level for hanging cabinets, installing countertops, doors or windows, or just about anything in your home that must be dead-level. 

    If you don't have or can't find your bubble or laser level, you can use the Speed Square for this, but you will need to have a string, twine, or chalk line on hand. Remarkably, using a Speed Square can be preferable to using a bubble level because you can measure the exact deviation down to the degree.

    On the Speed Square, locate the groove marked as 'Pivot." Place the Speed Square on the material with the pivot end up. Drape a string (such as a chalk snap line) over the Speed Square, resting it in the pivot groove. Weight the hanging end of the string with a light weight such as a bolt. If the work material is level, the string will hit the 45-degree mark. 

  5. Use a Speed Square to Cut 2x4s Square

    Cutting 2x4s is one of the most common activities in home improvement, which you will use for finishing basements, building walls, and similar projects.

    The ability to squarely cut 2x4s is a classic Speed Square maneuver and is well worth the price of the tool just for this. Rest the square's lipped fence over the 2x4. Hold the square firmly. Cut against the square with a power saw, making sure that the saw's fence slides along the square's fence. Do not let the saw blade run against the square.

  6. Use a Speed Square to Mark Boards for Ripping Wood

    Cutting laminate or engineered wood floorboards is made easier with a Speed Square. The Speed Square provides you with the ability to run long pencil marks parallel to the edge of the board. These marks can be between 3/8-inch to 3 1/2 inches from the edge of the board.

    Lay the Speed Square on the board, with the lipped fence over the edge. Place your pencil in the Speed Square's so-called Diamond cutout (for 3 1/2 inches) or in 1 of the 10 notches located in the triangular cutout (for 3/8-inch to 3 inches). Use a regular pencil, not a carpenter's pencil. Slide the square down the length of the board, drawing the line as you go.

  7. Use a Speed Square to Square Out Cabinets

    You can use a Speed Square to square up a kitchen cabinet against another cabinet or the wall. Bathroom cabinets, too, may be squared.

    Because the Speed Square is so versatile, you may forget that it is still a square. A Speed Square is best at squaring up smaller, shorter things rather than walls because it is only 7 inches long (though Swanson also does offer a 12-inch version). For squaring up walls and rooms, you need at least a carpenter's square. Better yet is a laser level that casts an "X" mark.

    Place the Speed Square against the two elements (such as wall and cabinet). If there is a gap, this means that the two elements are not square with each other.

  8. Use a Speed Square to Readjust a Saw

    The Speed Square isn't just for squaring up work materials; it can be used for checking square on tools, as well. There are times when you have adjusted your circular power saw so that its blade runs at an angle other than the usual 90 degrees. Adjusting the saw back to 90 degrees by consulting the saw's markings isn't always accurate, especially for older tools. 

    With the tool unplugged, rest one side of the Speed Square against the side of the blade. The other side of the square should rest against the bottom of the saw. Readjust the saw so that it is square against both sides of the Speed Square.

Metal speed square laying on wooden surface closeup

The Spruce / Margot Cavin