How to Measure Angles for Trim

Obtaining the Perfect Trim Joint Can be Tough when Corners are Not Square

By Mark J. Donovan

When installing baseboard trim it can be difficult to obtain perfectly mitered corners due to the fact that walls are rarely square. Simply cutting two pieces of adjoining trim at 45 degree angles frequently doesn’t cut it.

Spaces between the trim pieces are often so visible that it looks like a hack job at best. As a result the question frequently comes up on how to measure angles for trim to get that perfect joint. Well the answer my friends, is as simple as running down to your local home improvement store and purchasing a carpenters bevel square and a protractor.

Also, for inside corners you can also cope the baseboard trim using a coping saw. See these short videos on installing baseboard trim and coping inside corners.

A Carpenters Bevel Square is similar to a traditional combination square however with the bevel square you can adjust the length of one of the arms and rotate it. With these two features you can use a bevel square to determine the angle of a corner and make perfect trim joints.

To measure an outside angle for baseboard trim place one of the arms of the bevel square up against one of the wall surfaces, and then rotate the other arm until it is flush with the adjacent wall. Then tighten the wing nut on the bevel square.

Place the bevel square up against the protractor and read the angle measurement off of the protractor. Next divide the angle measured by two to determine the setting on your miter saw. So say for example you measured 86 degrees on the carpenters bevel square. Dividing this number by two, results in an angle measurement setting on the miter saw of 43 degrees.

After cutting each piece of trim to 43 degrees place them up against the wall and confirm that you achieve a perfectly fitted joint.

For measuring angles for trim on inside corners the process is nearly the same. Simply place the carpenters bevel square up against the inside corner and spread the arms until each arm is flush with its respective wall surface.

Then tighten up the wing nut and measure the angle using the protractor. Again, divide the angle measurement by two and set the miter saw to this angle. Finally, cut each piece of trim and place them against the walls to confirm that you have formed the perfect inside corner joint.

Want to end baseboard trim along the length of a wall? Then watch this short video on how to end baseboard trim on a wall.

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For information on installing Window and Door trim see’s  Installing Interior Window Trim Ebook and  Installing Interior Door Trim Ebook.  These Ebooks are loaded with pictures and provide easy to understand, step-by-step instructions, on how to install interior window and door trim.

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