Trim and Molding Calculator
Linear feet, boards, and cost — with room layout diagram
Trim Type:
Baseboard: deducts door openings only. Runs under windows.
Room Dimensions (ft)
Room Trim Layout
Top-down view showing trim placement along walls
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Frequently Asked Questions
How do I calculate linear feet of baseboard?
Add all wall lengths to get room perimeter. Subtract door widths (baseboard does not run across doorways). Add 10% waste. Divide by board length to get board count. Do NOT subtract windows — baseboard runs under windows.
Does baseboard go under windows?
Yes. Baseboard trim runs continuously along the floor under windows. Only doorways interrupt baseboard. Crown molding, however, runs over door openings (above the door casing).
How much waste should I allow for trim and molding?
Baseboard in rectangular rooms: 10%. Crown molding (requires complex angled cuts): 15-20%. Rooms with many corners or bay windows: add 5-10% extra. When in doubt, buy one extra board as a buffer.
What is the standard baseboard height?
3.5 to 4.5 inches is standard for 8-foot ceilings. Taller ceilings call for taller baseboards: 5.5 to 7 inches for 9-10 foot ceilings. Crown molding is typically 3.5 to 5.5 inches wide.
How do I cut trim for inside corners?
There are two methods: mitre joint (both pieces cut at 45° toward the corner) and cope joint (one piece is cut square, the other is coped to fit over it). Cope joints are preferred by professionals as they stay tight when wood expands or contracts.
How long are standard trim boards?
Most trim lumber is sold in 8, 12, or 16 foot lengths. 8-foot boards work for most walls. 12 or 16-foot boards reduce seams on long walls. Seams should be staggered and always land on a stud.