Perimeter = 2 × (length + width) — and why baseboard and crown deduct differently
A rectangle’s perimeter is 2 × (length + width): a 14 × 12 ft room is 52 LF. The deduction depends on the trade — baseboard skips a 3 ft doorway (52 − 3 = 49 LF), but crown runs over it and keeps the full 52 LF.
What this diagram shows
A room shown in plan, 14 feet by 12 feet, with the perimeter figured as 2 times 14 plus 12, which is 52 linear feet of edge. A 3-foot door opening is drawn in the bottom wall. Two take-offs come from the same 52-foot loop. Baseboard subtracts the doorway, because no trim runs across the opening, so 52 minus 3 leaves 49 linear feet. Crown or cornice runs continuously over the door and is not deducted, so it keeps the full 52 linear feet. The perimeter feeds baseboard, crown, chair rail, fence, gutter, and deck rail — subtract door openings for base, but keep the whole loop for crown.
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