Crown Molding

Crown molding encapsulates a large family of moldings which are designed to gracefully flare out to a finished top edge; generally used for capping walls, pilasters, cabinets; used extensively in the creation of interior and exterior cornice assemblies and door and window hoods.

In recent times, crown moldings have generally made their appearance as mostly decorated plaster or wooden trim where walls meet ceilings.


Crown molding is typically applied along the seams where ceiling meets wall. Usually it is not placed flush against the wall nor against the ceiling. Instead, when viewed from the molding's end, it, the ceiling, and the wall form a triangle. This adds a difficulty to the installation process, namely the need for complex cuts to form corners where two walls meet.

There are two common ways to fashion inside corners. One is to use a compound miter saw to cut the ends of the corner pieces along two axes simultaneously. The other, called coping, is a two step process, first to cut a simple miter and then to use a coping saw to undercut the miters.

Another way and the easiest way to install crown molding is by using crown corner blocks. This eliminates the need for miter cuts or coping; the molding is installed with a straight flat cut.

Many different companies now manufacture crown molding in materials such as plastic and foam. These typically are offered with corner blocks, and are popular with DIY home improvement enthusiasts.

Using a coped joint for interior corners saves you the trouble of having to determine and cut the exact inside degree measurement since most corners are not exactly 90/45 degrees. Outside corners must be mitered, but use care because not all outside corners measure true. Measure and cut accordingly. If the angle is not exactly 45/22.5 degrees use a corner measureing devise or piece of scrap crown molding to obtain the right measurement before you make your final cut.

Angle calculations

The calculation of the angles to cut crown molding is affected by the angle that the plane of the molding makes with the walls. Crown molding is usually sold in either a 45 degree or 38 degree format, so correct angle determination should be made before attempting to cut the molding.

The formula used to calculate the angle to make the cuts in a spreadsheet is:

* Cell 1 - slope a

* Cell 2 - \frac{A_{15}\times\pi}{180}

* Cell 3 - slope b

* Cell 4 - \frac{C_{15}\times\pi}{180}

* Cell 5 - wall angle

* Cell 6 - \frac{E_{15}\times\pi}{180}

* Cell 7 - \arctan\left

* Cell 8 - \frac{G_{15} \times 180}{\pi} = Miter Angle

* Cell 9 - \arctan\left

* Cell 10- 90-\frac{I_{15}\times180}{\pi} Bevel Angle in degrees

To simplify the cutting process, software can be used to accelerate the calculation process.

crown molding: Published with permission from Wikipedia, the free encyclopedia