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.