A measure of how tightly a carpet is packed. In machine-made carpet it describes the fibers in the pile and is calculated by multiplying the face weight by 36 and dividing by the pile height; higher density generally indicates better durability and performance. In hand-knotted rugs it means knot density (KPSI, knots per square inch), counted on the back and averaged over several areas (150 KPSI is about 23 knots per cm²). Like image resolution, higher density allows finer curves and sharper designs, usually with a lower-trimmed pile and more labor, but it is not the sole measure of quality: bold geometric village rugs are made at low to medium density.
The height of a rug's knotted pile, measured from the back of the rug to the top of the pile with a ruler or caliper, so the foundation is included. One dealer scheme sorts it into low (1/8 to 1/4 in, or 3.2 to 6.4 mm), low-medium (1/4 to 1/3 in, or 6.4 to 8.5 mm), medium (1/3 to 3/8 in, or 8.5 to 9.5 mm) and high (1/2 to 5/8 in, or 12.7 to 15.9 mm). The final trim sets it: sharply detailed, densely knotted rugs, including silk and silk-and-wool pieces, are cut low, while coarse ones with large designs, such as Heriz and Gabbeh, keep a taller pile. A higher pile feels more cushioned, and a medium-to-high pile suits busy areas and heavy furniture; a lower pile clears doors, absorbs less humidity, traps less dust and vacuums more easily.
The cutting back of a rug's knotted pile with shears. Weavers trim it lightly every few inches (roughly every 5 to 10 cm) of knotting so the pattern stays visible, and a final trim after the rug comes off the loom sets the finished pile height. Finely knotted rugs, such as silk Tabriz and other silk and silk-and-wool pieces, are cut short so that sharp detail shows, while rugs made to look antique, such as Kazak and Oushak-style pieces, are deliberately cut short so they feel thin and look aged.
The last production stage of a hand-knotted rug, after all knotting is done. The rug is taken off the loom, its pile is sheared to an even surface that fixes the final pile height, and it is washed professionally, sometimes with a spell in direct sun to calm colors that are too strong. Stray fibers are then trimmed away, and the rug is inspected for flaws before it goes to market.
Loss of pile height from use, where the wool has been walked short or away entirely, typically in a hallway, entryway or other high-traffic path, and in a badly worn rug the foundation begins to show. Even wear across the whole surface is the normal pattern on an older rug and is what buyers look for, whereas patchy wear, with short or bare zones beside fuller pile, weakens those spots and makes further damage likely, which matters most for a rug meant for heavy traffic. Rotating the rug periodically spreads the wear. Wear alone does not date a rug, since some new rugs are finished low to look old and some antiques keep a full pile.
A category of carpets with extremely low or non-existent pile height, including flat-weaves and certain low-profile commercial carpets. These floor coverings offer durability, easy maintenance, and accessibility benefits while providing sound absorption and comfort underfoot. Popular in high-traffic commercial spaces, healthcare facilities, and modern residential interiors where a minimal profile is desired.