How to Figure Out Corner Cuts for a Baseboard

Measure interior corners that are 90 degrees by first cutting a piece of baseboard to the length of the wall. Trim the baseboard’s end or ends that meet interior 90-degree angles at a 45-degree angle on a mitre saw. The baseboard’s back should be the longest, forming a point.

Measure outside corners by laying a piece of baseboard against the wall with one end flat with the opposite corner and the other end extending past the outside corner. Make a mark on the baseboard’s back where it extends past the adjacent wall. Make a second mark on top of the baseboard pointing outwards in the direction of the mitred corner. Cut boards with outside 90-degree corners at a 45-degree angle with the front of the baseboard creating the longest point.

Identify corners that are distinctly different from 90-degree corners for further measuring. An angle-measuring tool determines the degrees of these corners. Divide the final number of degrees by two to determine what degree to cut the mitre joints.

Test mitre joints before installing the baseboard by laying the boards against one another ensuring a tight fit. Trim joints as needed to get the correct fit. Boards that have a small gap can be filled with a small amount of caulk.