How to Cut 45 Degree Angle Cuts on Wood Trim

Updated February 21, 2017

Installing wood trim is one of the final jobs in finishing the interior of the home. Its job is to provide a smooth transition between walls, windows, and flooring. When cutting trim for 90 degree corners, you are required to cut each board with a 45 degree cut. This joins the two boards with one uniform joint. Cutting these boards is simple if you understand basic geometry. The proper tool for this job is an electric mitre saw.

Measure the wall from corner to corner where the trim is installed with a measuring tape

Transfer this measurement to the trim and mark the cut line with a carpenter's square and pencil.

Adjust your mitre saw to make a 45 degree cut. This is typically done with an adjustment mechanism on the back. Open the mechanism and angle the mitre saw until its gauge is aligned with the 45 degree marking and lock in place.

Align the trim's pencil line with the mitre saw's cut line and hold the trim in place with one hand. Make sure the hand holding the trim is sufficiently away from the blade during operation.

Activate the mitre saw with the other hand and guide the blade slowly into and through the wood.


Always wear eye protection when using a mitre saw.

Things You'll Need

  • Measuring tape
  • Carpenter's square
  • Mitre saw
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About the Author

Bob White began his writing career in 2006. Working in sales, he was a technical writer tasked with responding to requests for proposal. White has a Bachelor of Arts in computer science and a diploma in home inspection. He has also worked in construction, landscaping and the pool industry for more than 15 years.