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How to Cut a Window Molding at a 45 Degree Angle

Updated February 21, 2017

Window moulding frames the outside perimeter of a home's interior and exterior windows, providing a polished look for the home. While exterior moulding is often cut in block fashion with straight cuts, interior moulding is usually installed with 45-degree angled cuts in the corner that essentially mimic the framing layout of a picture frame. While cutting a 45-degree angle using a mitre saw is a simple process, you can still measure and make an accurate 45-degree angle cut with a protractor or even using only a measuring tape.

Measure the window with a measuring tape and mark the moulding with a pencil where the inside of the moulding will sit even with the corners of the window.

Place the moulding on a flat surface in front of you so that the outside edge of the moulding is on your left and the inside edge of the moulding is on your right.

Position a 45-degree protractor so that the 90-degree portion of the protractor fits against the outside edge of the moulding. Position the angled portion of the protractor so that the angle starts at the inside mark on the moulding and extends upward and to the left toward the outside edge of the moulding.

Draw a line on the moulding along the angled portion of the protractor.

Repeat the process at your mark on the other end of the moulding, but position the protractor so that the angle runs down and toward the outside edge, rather than up and toward the outside edge.

Cut the moulding with a handsaw using a fine-tooth blade to avoid splitting the moulding.

Measure the window and mark the moulding where the inside of the moulding will sit even with the corner of the window.

Place the moulding on a flat surface in front of you so that the outside edge of the moulding is on your left and the inside edge of the moulding is on your right.

Measure the width of the moulding. Make sure you take an exact measurement. Do not round.

Place a T-square across the width of the moulding at your mark on the inside of the moulding and make a corresponding mark on the outside edge of the moulding.

Measure from the outside mark you made in Step 4 up the moulding the exact measurement of the width. Make a mark on the moulding at this spot. For example, if the width of the moulding is 2 inches, then measure 2 inches up the outside edge of the moulding from the mark you made in Step 4.

Place a ruler on the moulding and draw a diagonal line from the top mark on the outside edge to your mark on the inside edge. The angle formed by this measurement will be exactly 45 degrees.

Repeat the process at your mark on the other end of the moulding, but measure from the outside edge down rather than up.

Cut the moulding with a handsaw using a fine-tooth blade to avoid splitting the moulding.

Tip

For simpler installation, consider purchasing decorative corner blocks that allow you to install moulding making straight cuts.

Things You'll Need

  • Measuring tape
  • Pencil
  • 45-degree protractor
  • Handsaw
  • Fine-tooth blade
  • T-square
  • Ruler
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About the Author

Kaye Morris has over four years of technical writing experience as a curriculum design specialist and is a published fiction author. She has over 20 years of real estate development experience and received her Bachelor of Science in accounting from McNeese State University along with minors in programming and English.