How to Read a Rug Specification: Knots, Pile and Materials Decoded

A rug specification sheet is a technical document that describes a rug's construction in measurable, reproducible terms. It allows a buyer to compare two rugs accurately without relying on adjectives, to specify exactly what they need in a procurement document, and to hold a supplier to an objective standard on delivery.

For architects and specifiers working on contract projects, the specification sheet is the foundation of the procurement process. It should accompany every sample approval and be referenced in the purchase order. Without it, disputes about quality on delivery are almost impossible to resolve objectively. Our contract quality page outlines the specifications we provide as standard for all commercial commissions.

Knot density is the most commonly referenced measure of a hand-knotted rug's quality. It is expressed as knots per square inch (KPSI) in markets that use imperial units, or knots per square decimetre (KPSD) in metric markets. A higher knot density allows finer design detail to be reproduced and generally indicates a more labour-intensive, higher-quality piece.

However, knot density alone does not determine quality. A rug with a moderate knot count in high-grade wool, with careful pile clipping and consistent dye work, may outperform a high-count rug in inferior fibre with uneven finishing. The specification should be read in conjunction with the material and construction method, not in isolation.

To convert between the two measures: one square inch equals approximately 0.645 square decimetres. A rug with 100 KPSI has approximately 155 KPSD. When comparing specifications from different suppliers using different unit systems, confirm the basis of measurement before drawing conclusions. Our knot density guide provides a more detailed breakdown of how density affects design fidelity.

Pile height is measured in millimetres from the base of the pile (the foundation) to the tip of the cut fibres. Specifications typically give a nominal pile height and a tolerance range, because hand-clipped pile is not perfectly uniform. A tolerance of plus or minus one millimetre is typical for well-finished handmade rugs.

Pile height affects the visual character of the rug (higher pile appears softer and more informal; lower pile appears crisper and more graphic), the tactile experience underfoot, the way the rug wears over time, and the cleanability of the surface. High pile can compress under heavy furniture; low pile resists compression but shows traffic patterns more readily.

For commercial specifications, pile height is often a performance consideration as much as an aesthetic one. Lower pile heights are generally preferred in high-traffic areas for ease of cleaning and even wear. Confirm the specified pile height with a physical sample rather than accepting a nominal figure.

The foundation of a rug consists of the warp threads (running lengthways, under tension on the loom) and the weft threads (running widthways, passed through the warp after each row of knots). The warp and weft materials affect the rug's dimensional stability, its drape, and how it wears over time.

Cotton warp and weft is the most common foundation material for Indian hand-knotted rugs. Cotton is dimensionally stable, does not stretch significantly with humidity changes, and provides a firm base for tight knotting. Wool warp and weft is traditional in some construction styles and produces a slightly softer feel but may be less dimensionally stable over time.

Silk warp and weft is used in the finest-quality Persian and Indian silk rugs. It allows very high knot densities because the fine warp threads can be set very close together. The resulting pieces are exceptional in design clarity but also more delicate and not suited to foot traffic. Our weaving page describes the foundation construction we use across our different product ranges.

The pile material specification should identify the fibre type (wool, silk, bamboo silk, cotton, or a blend), the fibre source where known (for example, New Zealand wool, Tibetan highland wool), and, for wool, ideally the grade. These details are significant because they affect the rug's durability, its lustre, its dye uptake, and its feel underfoot.

Blended piles are common and not inherently inferior. A wool and silk blend, for example, combines the durability of wool with the luminosity of silk. A bamboo silk and wool blend offers similar visual qualities at a more accessible price. What matters is that the blend is described accurately and that the proportions are specified, since a "wool and silk" rug could be anything from 95 percent wool to 95 percent silk without further qualification.

If the specification refers to yarn count or spinning method, these are further indicators of the fibre's quality and the density achievable. Discuss with the supplier if you need clarification on how a specific fibre specification was derived.

Handmade rugs are produced by hand on looms that flex slightly under tension, and the finishing process (washing, stretching, and blocking) further affects final dimensions. A rug specified at 8x10 feet will not measure exactly 8x10 feet. Industry-standard tolerances are typically plus or minus two to three percent in each dimension.

For commercial projects where precise fitting is required, specify the tolerance explicitly and confirm with the supplier that they can hold it. Alternatively, allow installation flexibility in the design: a rug in an open floor plan that is ten centimetres smaller than specified is far less problematic than one that must fit into a recessed architectural feature.

Finishing details that should appear in a complete specification include the type of selvedge (overcast, bound, or fringed), the fringe treatment if any, and the washing method (hand-washed, machine-finished, or chemical wash). Each finishing choice affects the final appearance and the care requirements of the piece. The rug process page illustrates our standard finishing methods.