How to Use a Protractor Angle Finder and Calculate Miter Saw Angles

by Joost Nusselder | Updated on:  June 20, 2021
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For carpentry purposes, house building, or just out of curiosity you must have thought, what is the angle of this corner. To find the angle of any corner you have to use a protractor angle finder tool. There are different types of protractor angle finder. Here we are going to discuss some easy and commonly used types of them, then how to use them properly.

How to Measure the Exterior Wall?

If you are using a digital angle finder, then line it up on the external surface of the wall or object. You will see the angle on the digital display.
Also read – Best digital angle finder, T Bevel vs Angle Finder

Line up

If you are using a non-digital type one then it should have a protractor and two arms attached in it. Use those arms to line up the angle of the exterior wall (flip the scale if necessary).

Take Measurement

Before lining up, make sure arms are tight enough so that it doesn’t move around after lining up. After lining up, pick up the angle finder and check the degree on the protractor.

How to Measure the Interior Wall?

To measure the interior wall or the interior surface of any object, you have to do the same as the exterior wall. If you are using digital ones then it should be easy. If you are using a non-digital type then you can flip the contraption by pushing on backward. Once it is flipped then you can easily line up with any inside wall and take a measurement.

Multipurpose Angle Finder

There are some analog angle finders that serve as more than just an angle finder tool. These angle finders have multiple numbers of lines on them and it can often get confusing. Empire Protractor Angle Finder is one of the multipurpose angle finders that are widely available. It is a small tool that can measure any angle from a leg of a small chair to a tall brick wall. It has four rows of numbers on it. Here I will break down what each line means. Even if you are not using this exact type of angle finder, after this you should be able to tell what your multipurpose angle finder’s row of numbers tells you.

Row 1 and Row 2

Row 1 and Row 2 are simple. These are standard degrees. One goes from left to right and the other one right to left and it has 0 to 180 degrees marked on each line. Usage It is most likely that you are going to use these two lines the most. You can line up the scale and take measurement of the obtuse angle and right angle at the same time from these two rows. There may be some time when you need to take measurements from left and again sometime from the right. They come in handy in these situations.

Row 3

This row is used for the settings of the miter saw. It can be quite challenging if you don’t have the knowledge about it. In some cases, the angle of protractor doesn’t line up with the angle of the miter saw. Here the 3rd row’s number comes in handy. But not all miter saw follows the 3rd-row numbers. So you have to be careful of which type of miter saw you have.

Row 4

You will see the 4th row’s 0 degree doesn’t start from any corner. It is because you can take measurements with the corner of your tool. When in the inside position, you will see an angle at the top of your tool. You can use this angle to measure the angle of your wall. Here you have to use the 4th-row degrees.

Crown Molding- Usage of angle finder and Miter Saw

Crown molding or any in kind of molding you have to measure and calculate the angle of the corner. Here the protractor angle finder comes to use. There are a few ways to calculate angles for your miter saw and use them in the molding.

Angle less than 90 Degree

Use your protractor angle finder to measure the angle of the corner you are going to be working on. If it is less than 90 degree then it is simple to calculate the miter saw angle. For less than 90 degrees angles, just divide it by 2 and set the miter saw angle to that. For example, if the corner is 30 degree then your miter saw angle will be 30/2= 15 degrees.

90 Degree Angle

For a 90 degree angle, follow the same instruction as less than 90 degrees or you can just use a 45-degree angle for this one since 45+45 = 90.

Angle Greater than 90 Degree

For an angle that is greater than 90 degrees, you have 2 formulas to calculate the miter saw angles. It is a bit more work than just dividing it by 2 but it’s easy none the less. It doesn’t matter which formula you use, the result will be the same for both.
Formula 1 Let’s say, the corner angle is 130 degrees. Here you have to divide it by 2 then subtract from 90. So your miter saw angle will be 130/2= 65 then 90-65= 25 degrees. Formula 2 If you want to use this formula then you will have to subtract your angle from 180 then divide it by 2. For example, let’s say the angle is 130 degrees again. So your miter saw angle will be 180-130=50 then 50/2=25 degree.


Q: Can I use an angle finder to draw an angle? Ans:Yes, you can use its arms to draw your angle after setting it to the preferred angle. Q: How to use angle finder for wood and baseboard? Ans: Line up the arms of your angle finder to the corner you want to measure and take the measurement. Q: Can I use a multipurpose angle finder for molding? Ans: Yes, you can. Make sure you have the right type of miter saw. Or you can use the formula after taking an angle. Q: Can I use one type of angle finder to measure both exterior and interior? Ans: Yes, you can. You just have to flip the angle finder to line it up according to the wall.


No matter what type of angle finder you use (digital or analog), make sure it doesn’t have any mechanical fault. If it is analog then make sure it is hitting the 90-degree point correctly and if it is digital check the screen if it says 0 or not. Angle finder is ideal for measuring angle and finding out miter saw angles. It is also easy to carry as it is not very big and convenient to use. So you should always have one in your toolbox.

I'm Joost Nusselder, the founder of Tools Doctor, content marketer, and dad. I love trying out new equipment, and together with my team I've been creating in-depth blog articles since 2016 to help loyal readers with tools & crafting tips.