There are many variations when looking at door trims, baseboards, or any decorative molding. As a general rule, door trim, or casing, will usually be about one-eighth of an inch thicker than baseboard.

How thick should door casings be?

The most widely used door casing is 2 1/4 inches in width, but can range up to 3 inches. The thickness is typically 1/2 inch but can range up to 3/4 inch thick for a more substantial casing or more detailed profile. Door casing and window trim are typically the same width and are interchangeable.

Can you use door casing for baseboard?

For baseboards, the bottom edge is square, where casing typically round the edges (which will not make as nice of a transition from the molding to the floor if installing over wood or tile). There's no real issue with it, except only that the more complex the profile, the harder it is to clean.