How to Use a Speed Square to Find Angles and Make Perfect Lines

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Make your next woodworking project easy with our beginner’s guide

Co-authored by Ryaan Tuttle and Eric McClure

Last Updated: August 3, 2025 Fact Checked

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Parts of a Speed Square

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Marking Straight Lines

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Measuring Angles

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Guiding Saw Cuts

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Video

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Q&A

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Tips

The speed square (also called a quick square or rafter square) is one of the most essential tools you’ll use as a woodworker or DIY hobbyist. Also known as framing squares or rafter squares, these tools are elegant in their simplicity and super helpful in their different use cases. In this article, we’ll show you how to use speed squares to mark straight lines, create exact angles, and guide saw cuts. Keep scrolling to learn more!

Speed Square: Quick Use Guide

Marking cuts: Hold the T-edge flush against any surface and use either of the remaining edges to draw a perfectly straight line.
Finding angles: Hold the T-edge flush and use a pencil to mark the desired angle on the wood. Pivot the speed square to line up with your mark and draw your line.
Assisting cuts: Hold the T-edge flush against the lip of the wood and use one of the other edges to brace your saw’s guide plate.

Section 1 of 4:

The Anatomy of a Speed Square

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The markings and edges on a speed square all serve different purposes. Home improvement specialist Ryaan Tuttle explains that a speed square has “all the framing measurements on it. It has all the conversion charts right on it. It can be used for framing a house. It will allow you to do roof and rafter layouts. It can be used to finish work. It can be used as a straight edge. It can be used as a 90-degree angle checker.”^{[1]
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Expert Source

Ryaan Tuttle
Home Improvement Specialist

Expert Interview} Here are the core parts:
- Ruler edge. Locate the inch markings. That’s the ruler edge—it’s designed to help you measure and serves as a straight edge for cutting with a saw or scribing lines.
- Diamond hole. The diamond hole is on the ruler edge. It’s the shape cut out at the 3.5 in (8.9 cm) mark. It’s exclusively for bird’s mouth cutouts—a type of cut roofers regularly have to make.
- Angle edge. On the line opposite the right angle, there are angles running from 0-90. These are degrees you use when using the speed square as a protractor.
- T-edge. The T-edge is the last side: it’s the side with the edge that pokes out to create a little ledge. You anchor the ruler edge using this side to create perfect 90-degree cuts.
- Line guide. Also called scribing notches, these are the little divots inside of the triangle closest to the right angle. Each divot is meant to hold a pencil tip. You put the tip in, then move the entire speed square along an edge to create a line.
- Hip-Val markings. These numbers are for roofers. The markings represent common rafter angles for hip and valley rafters.
- Common markings. These are also for roofers. The markings are “common” angles for rafters.

Section 2 of 4:

Marking Straight Lines with a Speed Square

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1
Position the lipped edge of the speed square against the edge of the wood. Identify the lipped fence, called a T-edge, and place it flush with the edge of the wood. When drawing lines, keep the lipped fence firmly pressed against the wood for best results. Use either side of the speed square, as both sides will have a lipped fence.^{[2]
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- The lipped fence allows you to brace the speed square flush with the wood, creating a straight or angled line that is proportionate to the wood's edge.
- Why use a speed square to mark lines? The speed square has three built-in straight edges, which makes it easy to make quick marks. It also features a built-in 90-degree angle and a built-in 45-degree angle, two of the most common cuts in woodworking.
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Use the speed square as a straight edge for horizontal lines. Use a pencil to draw a square, or perfectly straight line down your piece of wood. Place the graphite of the pencil against the base of the speed square and slowly trace the line. Make as many straight marks as your project calls for and redo the lines if you make a mistake.^{[3]
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- Straight lines are necessary for projects that call for shortening pieces of wood, especially when accuracy is a must.
- Using a pencil to draw the line will allow you to erase the mark if you make a mistake or need to change your plan.
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Or, use the scribing notches to draw long vertical lines. If you need to draw a parallel line along a length of wood, use the line guide inside the triangle near the 90-degree angle. Measure how deep you want the line to be and then hold the T-edge flush against the wood. Put your pencil inside the notch that matches the depth you want and press it into the wood. Then, drag the pencil and square together along the wood to draw your line.^{[4]
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- These lines are helpful if you need to trim the width of wood boards.
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Draw 45-degree angles using the angle edge. Keep the lipped fence of the speed square flush with the wood and use a pencil to trace a line down the hypotenuse, or longest part, of the speed square. This is the angle edge because it lists all of the angles you can make. Trace the hypotenuse to create perfect 45-degree angles, especially during projects that call for perfectly angled pieces of wood.^{[5]
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- 45-degree lines are necessary for many projects, especially when it comes to roof rafters and other sloped pieces of wood.
- The hypotenuse is the longest line of the speed square, connecting the base and the lipped T-edge.
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Measure distances between marks with the ruler. With the ruler on each face of the speed square, measure distances between markings for accuracy. Take measurements for straight lines, as well as for 45-degree marks.^{[6]
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- The ruler on the speed square will allow you to make accurate, perfectly measured marks on pieces of wood.

Section 3 of 4:

Finding and Marking Angles with a Speed Square

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1
Press the fenced lip of the speed square flush with the wood. Keeping the T-edge side of the speed square flush with the piece of wood you are using will keep the protracted angles accurate during later stages. Position the base of the speed square on the wood so that you can make the mark in the correct location.^{[7]
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- You will only need to keep one point of the speed square flush when pivoting it, but it is important to begin flush with the wood.
- Why use a speed square to find or mark angles? Since cutting wood often requires carefully-marked cuts in a straight line, it helps to have the tool you need for locating and marking angles attached to the thing you can use to cut and draw straight lines! Basically, a speed square saves you from swapping out tools while you’re in the middle of measuring.
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Use the pivot point to set the speed square to the appropriate angle. Holding the pivot point on the speed square, which is located at one end of the lipped fence, rotate the speed square until your desired angle matches the end of the wood. Line up the straight edge of your speed square with the mark you made.^{[8]
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- The speed square will have ruler-like numbers on the hypotenuse side, which represent different angles ranging from 0 to 90. This is how you measure the size of your angle.
- What if my angle is greater than 90 degrees? Mark 90 degrees first, then subtract 90 from your desired angle and add it to the end. So, if you want to mark off 105 degrees, draw a 90-degree angle with your straight edge. Then, flip the speed square over and mark off 15 degrees from the line you just drew.
Once your angle has been aligned, trace the base, not the hypotenuse, to create your angled mark. Trace slowly and accurately, taking care to create a thick, visible line with your pencil. Once the mark has been made, erase the graphite if you feel like you've made a mistake and try again.^{[9]
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Reposition the speed square and draw a straight line. In order to gain an accurate representation of your angle and check your mark, position the base of the speed square with the end of the mark. Trace the base of the speed square to draw a straight line, allowing you to visibly identify the angled mark.^{[10]
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- How accurate are speed square angles? Tuttle says that speed squares are extremely accurate within up to a half-degree.^{[11]
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  Ryaan Tuttle
  Home Improvement Specialist
  
  Expert Interview} If you need more accuracy than that, you’ll have to use a digital angle finder.

Section 4 of 4:

Guiding Saw Cuts with a Speed Square

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1
Clamp the piece of wood to a table. For safety purposes, it is important to secure the wood to the table. Use medium-sized C-clamps that allow you to screw and secure the wood to the table. Tighten the clamps until the wood does not move when pressed on or pushed. Do not clamp the wood too tightly, as this could damage or split the wood.^{[12]
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- Stop securing the piece of wood as soon as it is secure and immovable.
- Why use a speed square to help cut? You don’t have to use a straight edge to make cuts with a saw, but if you’re prioritizing a clean cut, it helps to have the straight edge to pin the guide plate firmly as you cut.
Using the lipped fence of the square, brace it firmly against the wood to ensure it doesn't move while cutting. Consider clamping the speed square to the wood if you are nervous about it moving during your cut.^{[13]
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Run a saw along the speed square. Slowly pass the saw along the wood, keeping it flush with the speed square while making the cut. The speed square will allow you to cut steadily and accurately because it is thicker than a framing square or combination square. Take care when operating a saw (wear goggles and avoid distractions).^{[14]
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- It is a good idea to take a few practice cuts before cutting the wood you need if you aren’t familiar with power saws.
- People typically use speed squares with circular saws or jigsaws, although any saw with a guide plate will work just fine.

Community Q&A

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How I find the degree of a cut when joining boards

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You can use the protracting method mentioned above and find the angle on the hypotenuse side of the speed square.

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What does a 2% slope in 48" equal?

Donagan

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The rise would be just under an inch.

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What is the purpose of a speed square when marking a staircase?

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Speed squares are more suited for framing, measuring, and marking cut layouts. For stair building, a framing square is a much better tool; with a few tweaks, it can become a production layout tool (and very accurate one).

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Tips

The speed square typically comes in two sizes: A 7 inches (18 cm) pocket version, which can travel in most portable tool kits, and a larger 12 inches (30 cm) version, which is often used for stationary work.

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Speed squares are also known as rafter squares, combination squares, and framing squares.

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