How to Trim Baseboard on Doors & Windows

Mark the reveal around the window or door. The reveal is the section of the jamb that will be visible. A typical reveal is about 1/4-inch wide. Use a level as a straightedge and draw a light pencil line around the window or door's jamb.

Measure the length of the window or door's top edge from the inside corners. Transfer this measurement to a piece of trim. Set a miter saw to a 45-degree angle. Lay the piece of trim under the cutting blade.

Swivel the blade to the right and make a 45-degree cut on the left-hand mark. Move the trim down. Swivel the blade to the left and make a 45-degree cut on the right-hand mark.

Lift the cut trim to the window or door's top edge. Line up the trim's bottom edge with the pencil line marking the reveal. Drive finishing nails through the trim with a pneumatic nailer to secure the trim in place.

Measure the length of the window or door's sides. Transfer this measurement to two new pieces of trim. Make a right-hand 45-degree miter cut on the trim you plan to install on the window or door's right side and a left-hand 45-degree miter cut on the trim for the left side. If you are trimming a window, miter the trim's bottom edges as well.

Lift the two trim pieces up to their respective sides. Push the mitered ends tightly against the top trim's mitered ends. If there is a gap, reset the miter saw and shave a little bit off the trim's end so the two pieces fit tight. Check that the reveal running down the sides is even. Secure the two pieces in place with finishing nails from a pneumatic nailer.

Measure the window's bottom edge. Transfer this measurement to a fourth piece of trim. Make a right-hand 45-degree cut on the right side and a left-hand 45-degree cut on the left side. Position the trim between the two side pieces and check for gaps. Check that the reveal line is even. Secure the bottom trim piece in place with finishing nails.