Calculating angles is an essential part of most woodworking projects. You’ll usually need to figure angles when building furniture, or starting any project that requires two pieces of plywood to fit together perfectly, like building frames (for doors, windows, or pictures), tables, or wall paneling.
There are two types of angles you can measure: standard angles and miter angles. Different tools are available to help you measure new angles, and to cut and trace an angle onto a new sheet of plywood for cutting.
Keep reading to learn how to figure angles for cutting wood and what tools you need.
How Do You Work Out Angles to Cut Wood?
Before measuring angles, you need to first work out the type of angle you need to cut: a standard angle or a miter joint. The tool you need to use will vary depending on the cut you need to make.
Cutting Standard Angles
Standard angles are considered any angles that need to be measured on a sheet of plywood. These angles are either measured before cutting, or to check an angle is correct on an existing cut of wood. Cutting standard angles in plywood can be done using any angling tool. Generally, the best tools to use are T-bevels (also known as bevel gauges), protractors, or digital angle rulers.
Cutting a Miter Angle or Miter Joints
A miter cut is when two pieces of plywood are cut at angles along the face or width of the board to join corners together perfectly. A true miter angle is when the two sheets are cut at 45-degree angles to form a 90-degree corner when positioned together.
Miter angles are usually required to cut skirting boards, coving, or furniture. The best way to measure a miter angle or miter joint is to use a site protractor (also known as a miter protractor). When cutting miter joints, you may need to use a miter saw table and miter clamps.
What Tools Do You Need to Measure Angles?
There are five main tools you can use to measure angles:
- A T bevel or bevel gauge
- A speed square
- A protractor
- A digital angle ruler
- A site protractor or miter saw protractor
Most tools can be used universally to measure any angle, except for miter angles, which should be found using a site protractor.
- Using a T Bevel or Bevel Gauge
A T bevel is a short, flat blade that swivels around and can be locked into place. It’s often referred to as an angle finder or a bevel gauge. These devices can be adjusted to help you figure angles in wood before cutting. You can use a bevel gauge to find a new angle, or to trace and transfer an angle measurement from a corner to a piece of wood.
To figure a new angle using a T bevel, you need to:
- Loosen the nut at the top that allows you to swivel the blade
- Move the blade until you’ve reached your desired angle
- Lock the angle in place by twisting the nut again
- Lay the bevel on your wood in the position you need to cut it
- Trace the angle using a pencil
- Remove the bevel and make your cut, as needed
To trace and transfer an angle measurement using a T bevel, you need to:
- Loosen the nut that allows you to swivel the blade
- Lay the bevel against the surface or in the corner you need the measurement of the angle
- Rotate the blade until it matches the angle perfectly
- Lock the angle in place by twisting the nut again
- Place the bevel on the surface you need to cut
- Trace the angle (using the inside of the bevel) using a pen or pencil
- Remove the bevel and cut the wood, as needed
- Using a Speed Square
A speed square is a right-angled (90-degree) triangle you can use to measure angles for cutting plywood. You can use a speed square to calculate 90-degree, 45-degree, and any other given angle. Many woodworkers also use a speed square to find a roof pitch or guide saw cuts.
Here’s how to use a speed square to measure angles:
- Lay the lipped edge of the speed square against the edge of the wood in the position you want to measure the angle
- Draw a straight line along the top of the speed square (at a perfect right angle from the edge)
- Pivot the speed square at the pivot point (labeled), using the numbers on the hypotenuse side to reach your desired angle
- Mark the angle with a pencil
- Draw a straight line along the base of the speed square to create your angled mark
- Reposition the speed square so the base lines up with the end mark
- Draw a straight line to measure your angle
- Using a Protractor
Using an old-fashioned mathematics protractor is not ideal for cutting wood because of its small size, which can lead to inaccuracies. However, it can still be used to measure angles for woodworking projects if it’s the only device you have. A protractor is a small semi-circle or full-circle device that allows you to measure acute (less than 90 degrees), obtuse (more than 90 degrees), and right angles (90 degrees exactly).
You can use a protractor to trace the angle you want onto a sheet of plywood, or you can use it to measure an existing angle in wood.
Here’s how to use a protractor to find a new angle:
- Mark your centerpoint where you’d like to measure your angle from
- Lay the protractor on the sheet of plywood you want to cut
- Align the centerpoint of the protractor to the position you want your angle to pivot from
- Find your angle measurement and mark it as accurately as possible with a pencil
- Remove the protractor and use the straight edge or a ruler to draw a line from the centerpoint to the angle measurement
- Cut along the line to achieve your angle measurement
Here’s how to use a protractor to measure an existing angle in a cut of wood:
- Lay the centerpoint of the protractor in the corner of the plywood cut (you can measure either corner in a slant of wood to give you the obtuse or acute angle)
- Using the measurements around the protractor, measure the point the wood ends with the angle measurement
- Record your angle
- Using a Digital Angle Ruler
Digital angle rulers are more advanced than most other tools on this list. These have two rulers connected together with a hinge and a digital display screen in the corner. You can use a digital angle ruler to measure existing angles or find a new angle.
Generally, digital angle rulers are one of the more accurate ways to measure angles, especially when the cut needs to be exact, as the display screen shows the angle to several decimal points.
Here’s how to use a digital angle ruler to find a new angle:
- Lay the tool on the wood in the position you need to make the cut
- Pivot the ruler until the display screen shows you the angle you need
- Use a pencil to mark the angle or draw a straight line along the edge of the ruler
Here’s how to use a digital angle ruler to measure an existing angle:
- Lay the tool against the angled cut
- Pivot the tool until the rulers perfectly align with both sides of the wood
- Use the display screen to record the exact angle
- Using a Miter Saw Protractor (Site Protractor)
Miter saw protractors (also called site protractors) are used to create miter joints and record miter angles. A miter angle is when you need to cut two pieces of plywood and slot them together once cut. For example, if you need to cut trim around a doorframe and the two pieces need to interlock.
Miter protractors have two scaled rulers with an inner and outer scale that you can use to measure the miter angle needed for each piece of wood.
Here’s how to use a miter protractor to measure the angles you need to cut:
- Place the miter protractor against the angle you need to measure (for example, if you need to measure the angle needed for trim around a bay window, place the protractor between the two sections of wall)
- Push the miter protractor so it sits flush against the two sections
- Remove the protractor from the corner (making sure not to move the two rulers)
- Record the number displayed on the scale labeled “outer” (this tells you the angle you need to cut for one piece)
- Record the number displayed on the scale labeled “miter” (this tells you the angle you need to cut for the other piece)
Summary: What Tool Do I Need to Cut Angles in Wood?
|Tool||What It’s Best Used For|
|T Bevel / Bevel Gauge||Figuring new angles or tracing and transferring angles|
|Speed Square||Measuring 90-degree or 45-degree angles|
|Protractor||Measuring acute, obtuse, and right angles|
|Digital Angle Ruler||Finding new angles or measuring existing angles|
|Mitre Saw Protractor / Saw Protractor||Cutting mitre angles or mitre joints|
Conclusion: Things to Remember
Remember, the most important things to do when finding the actual measurement of an angle are to:
- Work out whether you need to measure an acute, obtuse, right, or miter angle
- Find the best tool to help you measure the angle you need
- After initially measuring and plotting the angle, check it again before cutting to ensure it’s perfectly aligned (remember the saying: measure twice, cut once!)