Carpet roll width drives seams — a room wider than the 12-ft roll needs a fill strip
Carpet comes off a fixed-width roll (12 ft is the US standard). Any room wider than the roll needs a second strip and a seam, so you buy more than the bare square footage. Run strips along the longer wall to keep seams short.
What this diagram shows
A plan view of a 15-foot-wide by 18-foot-long room shows how broadloom carpet is cut from a 12-foot-wide roll. One full 12-foot-wide strip covers most of the floor and a 3-foot-wide fill strip covers the rest, leaving one seam that runs the full 18-foot length of the room. The strips are run along the longer wall to keep the seam short, and a formula shows strips equal the room width divided by 12 feet rounded up — 15 divided by 12 rounds up to 2 strips and 1 seam. Because of the fill strip you actually buy 18 by 12 feet, about 24 square yards, more than the bare 270 square feet of floor. A 15-foot-wide roll would carpet this room with no seam.
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