Walls & Trim guide
How to measure for baseboard and crown molding
Trim is measured by length. Baseboard follows the floor and stops at door openings; crown molding follows the ceiling and runs straight past them. Either way, convert the net length into the piece size sold at your store.
Walk the room with a tape
Measure each wall and mark doorways, built-ins, cabinets, and openings where trim stops. Add the wall lengths rather than assuming the room is perfectly rectangular. Note every outside corner and return.
Crown: run = perimeter + soffit and bump-out returns
Pieces = round up(length × (1 + allowance) ÷ piece length)
Worked example
A 12 × 10 ft room has a 44 ft perimeter. With 6 ft of door openings, baseboard covers 38 ft. Adding 10% gives 41.8 ft; in 8 ft pieces that is 5.23, so buy 6 pieces. Crown molding for the same room runs the full 44 ft; with 15% for corner cuts that is 50.6 ft, or 5 pieces at 12 ft.
Allow for joints and cuts
Longer pieces reduce joints but are harder to transport and handle. A modest allowance covers damaged ends and unusable offcuts; add more when the room has many corners or you are matching an existing profile.
Why crown gets more allowance
Crown sits at an angle between wall and ceiling, so each corner takes a compound miter or a cope, and a miscut piece is often too short to reuse. Home improvement retailers commonly suggest ordering 10–15% extra. Decorative corner blocks let you make square cuts instead and reduce waste.