Guide · For the trade
Carpet density: the number on the spec sheet that predicts how a carpet wears
Carpet density is the face weight in ounces per square yard multiplied by 36 and divided by the pile height in inches, giving ounces per cubic yard of pile: a 40 oz carpet at a 0.40 inch pile is 3,600, the same 40 oz at 0.25 inch is 5,760. A density of 3,000 is the floor for a residential spec, 4,000 to 5,000 is where a hall or a family room should sit, and 5,000 and up is commercial. It is the single best predictor of how a cut pile will resist crushing, because it measures how much yarn is packed into the space a foot lands on.
This guide is for the designer or the junior learning how to read carpet specs: what density is, how to calculate it when the sheet leaves it off, how it relates to face weight and twist, and what the mills in our library publish. The companion pages are the carpet face weight guide and the carpet pile height guide.
What carpet density measures, and why it beats face weight
Face weight is how much fiber is on a square yard. Pile height is how tall that fiber stands. Density is the two together: the same 40 ounces spread over a 3/4 inch plush is loose and crushes, while over a 1/4 inch loop it is packed and does not. A client who has read that "60 oz is better than 40 oz" is comparing weights and missing the height; a 60 oz shag at 1 inch is a density of 2,160, a bedroom carpet, and a 40 oz cut pile at 1/4 inch is 5,760, a hotel corridor. Gauge and stitch rate (tufts per inch across and along) and twist, covered below, finish the picture.
The carpet density formula, and a worked example
- Take the face weight from the spec sheet, in oz per square yard. Not total weight, which includes the backing and inflates the result.
- Take the pile height in inches; on a cut-and-loop, use the average or the sheet's stated figure.
- Multiply the face weight by 36 and divide by the pile height.
A tufted nylon at 34 oz with a 0.40 inch pile: 34 times 36 is 1,224, divided by 0.40 is 3,060, a bedroom or living room carpet. A wool loop at 48 oz with a 0.30 inch pile: 1,728 divided by 0.30 is 5,760, a stair and hall carpet. A commercial loop at 24 oz with a 0.15 inch pile: 864 divided by 0.15 is 5,760 again, which is why a 24 oz commercial carpet outlasts a 50 oz plush in a corridor.
A carpet density chart for specifying
| Density (oz per cu yd) | Reads as | Specify it for | Typical construction |
|---|---|---|---|
| Under 2,500 | Low; crushes in any lane | A guest room at most | Long shags, soft plushes, budget polyester |
| 2,500 to 3,500 | Residential standard | Bedrooms, living rooms, home offices | Tufted cut pile at 30 to 40 oz, 1/2 inch pile |
| 3,500 to 5,000 | Residential heavy | Halls, stairs, family rooms | Dense cut pile, loop, wool Wilton at 40 to 50 oz |
| 5,000 to 7,000 | Commercial | Corridors, offices, hospitality, multifamily common areas | Level loop and low cut pile at 20 to 32 oz; woven Axminster |
| Over 7,000 | Severe commercial | Airports, lobbies, exit stairs | Tight loop at 1/8 inch or less |
In the library, Milliken prints the density on its residential nylon sheets, in a 2,500 to 6,000 range by line, with its 40 oz cut piles at the top of that range; Masland publishes face weight and pile height on most sheets, and the formula fills the gap. Wool mills rarely print density, so for a Wilton or a hand-loomed wool it is calculated from the sheet, or from the sample with a ruler and a scale.
Carpet twist, the second number
Twist is the number of turns per inch put into a cut-pile yarn before it is heat-set, written as TPI. A standard cut pile is 3.5 to 4 TPI; a premium texture or a frieze is 5 to 7 or more. Higher twist means the yarn tip stays closed and springs back from a footprint instead of blooming open and matting, which is why two carpets of equal density can look different after a year. Twist does not apply to a loop pile, and it matters less in wool, whose crimp does part of the job. On a spec sheet it appears as "twist" or "TPI"; a sheet that omits it on a cut pile is worth a question to the mill. For a family room or a stair in a cut pile, ask for 5 TPI and up with a density over 3,500; the frieze carpet guide covers the high-twist end.
Reading the rest of the sheet
The lines that complete a durability judgment are: fiber (nylon type 6,6 and wool resist crushing; polyester and polypropylene do not, whatever the density); construction (woven Wilton and Axminster lock the yarn into the backing and outlast a tufted carpet at the same density); gauge and stitches per inch; the TARR appearance retention rating on a commercial sheet (Heavy 3.0, Severe 3.5); the texture retention warranty on a residential one (10 to 20 years); and the flammability line, Class I at 0.45 W/cm2 or more. The how to specify carpet guide turns these lines into a written spec, and the carpet wear rating guide explains the test behind the TARR number.
Density of the pad is a separate number
High density carpet pad is a different measurement: pad density is pounds per cubic foot, 6 lb or 8 lb for rebond, 32 oz per square yard for felt. Match the pad to the carpet: 7/16 inch 8 lb rebond under a residential cut pile; 1/4 to 3/8 inch dense felt, rubber or 32 oz pad under Berber, loop, Wilton and stairs; commercial carpet glued direct or over a thin firm cushion. A dense carpet over a soft pad flexes at the backing and loses its advantage; the carpet pad types guide pairs them.
Questions designers ask
Is a 60 oz carpet good?
Only if its pile height is under about 0.60 inch, which puts the density at 3,600 or more. A 60 oz plush at 3/4 inch is 2,880 and will crush in a hall; a 60 oz wool at 1/2 inch is 4,320 and is excellent. Ask for the pile height before judging the weight.
How is a 10 by 12 foot room quoted, and does density change the quote?
By the square yard: a 10 by 12 room is 13.3 square yards plus 10 to 15 percent for cutting and seams, about 15 yards of 12 ft goods. Density moves the price per yard because more fiber in less height means more yarn; net pricing is quoted to approved trade accounts by style.
Is a 25 oz carpet good?
In a commercial loop at 1/8 to 3/16 inch, a 25 oz carpet is a density of 4,800 to 7,200 and is built for a corridor. In a residential cut pile at 1/2 inch it is 1,800 and belongs in a closet. The weight means nothing without the height.
Is a 6 lb or an 8 lb carpet pad better?
8 lb, under any residential cut pile; it supports the backing and most texture retention warranties require it. 6 lb is a builder pad that lets the carpet flex and shortens its life, and it is not a pad for a stair or a loop at all.
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