How to Calculate Angles for a Miter


The miter cut is necessary when joining two boards at an angle-- most often when joining the trim around a door or window, the corners of baseboard and molding or in building a picture frame. For inside and outside base corners, the angles will be 90 degrees, but not always. In order to make the corner you need to cut two pieces of material at a 45-degree angle. When you join them together they make the 90-degree corner. If the corner is not exactly square, you can fix that easily.

Step 1

Use your protractor to measure the angle of the corner. You must know whether it is smaller or greater than 90 degrees before you start cutting.

Step 2

Divide the angle by two. You have to make two cuts to equal the entire angle so the finished joint will look attractive. A miter box will make 45-degree and 90-degree angle cuts.

Step 3

Transfer the cutting line onto both pieces if you do not have a protractor, overlapping the ends of your two boards so they fit the corner. Mark a line along their intersection from the outer corner to their inner corner with your pencil.You can actually nail them together and cut both pieces at the same time. This will give you a perfect pattern for marking the finished pieces.

Step 4

Use an adjustable miter saw if your corner angles are slightly imperfect, adjusting only one of your corner pieces for a snugger fit. Coping moldings is a more refined than mitering for achieving difficult fits.

Tips and Warnings

  • Remember that every bend has two angles. One on each piece making the bend.

Things You'll Need

  • Protractor
  • Miter box
  • Adjustable miter saw
  • Calculator
  • Pencil


  • Woodweb: Perfect Miters
  • Kelleher Corporation: Cutting Miters
Keywords: miter cuts, mitre cuts, calculating miter angles

About this Author

After attending Pasadena City College as a business major, Ron Sardisco spent 35 years studying small business and organizational behavior. More than 20 years as a banker, 10 years as a small business owner and five years as a business adviser fuel his passion for writing and mentoring others. An award-winning photographer, he was also a contributing columnist to the "Antelope Valley Press."

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