By taking into account the room dimensions, such as ceiling height, as well as the existing trim, you can pick the appropriate sizes for moldings and casings.
Function
Carpenters use the term "trim" to refer to ceiling moldings, chair rails, baseboards, door and window casings and similar decorative elements. However, trim isn't just for decoration; it protects walls and covers wall openings. For example, the casings that frame doors and windows cover the gaps between the window framing, or jamb, and an adjacent wall. Baseboards protect the bottoms of walls from damage by mops and vacuum cleaners. It's necessary to consider all of the trim in a room to choose the proper sizes for moldings and casings.
Standard Ceilings
Baseboards and ceiling, or crown, moldings can overpower a room if the ceiling height isn't considered. For example, standard ceilings that are 8 feet high should have crown moldings that are 2-1/2 to 6 inches high, according to This Old House. The Home Tips website recommends that baseboards be no more than 6 inches high in rooms with 8-foot ceilings. The wider the trim, the smaller a room appears. Therefore, small rooms with low ceilings can feel cramped when crown moldings and baseboards are too large.
High Ceilings
Moldings and baseboards should be at least 6 inches in height in rooms with very high ceilings, according to the Home Tips site. This Old House recommends that rooms with 9- or 10-foot ceilings need crown moldings that measure 3 to 7-1/2 inches or 3 1/2 to 8 inches high, respectively. Follow the same guidelines for the widths of door and window casings in these rooms so that standard-size windows don't look too small for the space.
Trim Thicknesses
The thickness of one type of trim can help you choose the appropriate thickness for other types. For example, a baseboard shouldn't be thicker than the casings that surround doors and windows in the same room, according to the Home Tips site. Furthermore, the vertical pieces of door and window casings shouldn't be thicker than the horizontal pieces they abut.