Thread count: what it does and doesn't tell you

Thread count is a simple sum. Take a square inch of fabric (2.54 × 2.54 cm), count the vertical warp threads and the horizontal weft threads in it, and add the two numbers together. A fabric with 150 warp and 150 weft threads has a thread count of 300. Nothing else is hidden in that number – not the type of cotton, not the staple length, and not how the fabric will look after its hundredth wash.

Why the number can be inflated

The finest fibres can be spun into thinner thread, and more thin threads fit into an inch. Physically, though, there is a limit: beyond a certain density no more threads will fit, and the fabric would be as stiff as paper. A figure of 800 or 1200 on the packaging is therefore usually arrived at differently: the manufacturer uses plied yarn – two or three fine yarns twisted into one thread – and counts each component separately.

A fabric with 300 two-ply threads can thus be labelled "600" on the packaging. The technical definitions used in measuring thread density (ASTM) count a plied thread as one unit. The US Federal Trade Commission has commented on the practice twice. In 2002, replying to the manufacturers' association ATMI, it said that any thread-count claim must have a "reasonable basis" and that it gives great weight to consensus test methods such as ASTM D3775. In 2005, according to trade press reports at the time, its staff stated that multiplying the actual thread count by the number of plies could mislead consumers, and considered a description along the lines of "300 thread count, two-ply yarn" not to be misleading.

In the European Union there is no specific rule on thread count for bed linen. Measuring thread density is described in the standard EN ISO 7211-2:2024, but the result is given in threads per centimetre, not as a single "marketing" number.

What a high number doesn't guarantee

On the packaging	What it really tells you	What it doesn't
Thread count	How densely it is woven	Fibre quality, durability, softness after washing
"Egyptian cotton"	Origin (if true)	That the fibre is extra-long staple
"100% cotton"	Fibre composition	Weave, yarn, finish

A dense fabric made from short fibre and plied yarn can be heavy, stiff and less breathable – and still have a high number on the packaging. Conversely, a simple percale of 200 to 300 threads made from long fibre can feel nicer and last longer.

What to ask instead

1. Which fibre? Long-staple and extra-long-staple cotton can be spun into a thread that is both fine and strong. More in the entry Staple length.
2. Single or plied yarn? If plied, what is the thread count with every thread counted once?
3. Which weave? Percale and sateen feel completely different at the same number.
4. What weight? The mass per square metre tells you whether the fabric is light or heavier – see Fabric weight (GSM).
5. Verifiable origin? For Egyptian cotton there is a licensed trademark – more in How to tell genuine Egyptian cotton.

How to check the number at home

Without a magnifying glass and a laboratory you cannot count it precisely. You can, however, make a rough estimate: pull a single thread from the edge of a sample and tease out its end with a needle. If it falls apart into two or three separate fine yarns, it is a plied thread. If the manufacturer states "1000 thread count" and the threads are three-ply, the real density is roughly a third of that.

It is worth asking the retailer for an answer. Where labelling has turned out to be false, it has not been about details: in 2016 the American retailer Target withdrew sheets labelled as 500-thread-count Egyptian cotton from sale after finding that its supplier had used other cotton.