Simple Solutions

How to Cut an Out of Square Miter Joint

By: Joe Truini

A 45° miter joint is the perfect means for joining two pieces of molding in a 90° corner (such as case molding around a window). Unfortunately not all such corners are exactly 90 degrees, so the miter joint has to be adapted to fit tightly. Here’s how to go about it:

  1. Nail the top piece of molding in place with a 45° angle cut.
  2. Line up the side molding so it’s even with the frame and overlays the top molding.
  3. Mark the inside and outside points on the side molding where it intersects the top miter joint.
  4. Connect the two points with a straight line and make the cut along that line.
  5. The result should be a tight fitting miter that matches the existing corner.


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3 Comments on “How to Cut an Out of Square Miter Joint”

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  • Tracy Says:
    January 18th, 2018 at 2:17 pm

    I just read a long, wordy piece about how to do this and was none the wiser after three readings. Watched your short, clear video and got it straight away. Thank you. Off to do my window trim now.

  • Jon Jones Says:
    October 15th, 2017 at 11:47 am

    Huge fan of the show! Thank you for making this show. It has given me confidence & new tools to do a lot of things to my home that I wouldn’t have done without seeing the show. I have a bunch more projects to go, however, I look forward to see what I can achieve next thanks to each of you. I trully enjoy each episode.

    Thank you all again for making this show happen!.


    Jon Jones
    Seattle, WA

  • Rosalyn Mcdermott Says:
    September 30th, 2017 at 2:18 pm

    we are trying to rebuild our deck stairs using composite material. We are trying to miter the border piece and are having monumental problems getting the corners to match well. We tried your technique and it didn’t work. HELP

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How to Cut an Out of Square Miter Joint