How to Specify Bed Linen Cloth: GSM, Thread Count and Yarn Count

GSM is the weight of a square metre of cloth in grams. Thread count is how many warp and weft threads sit in a square inch. Yarn count is how fine the yarn itself is. They measure three different things, and none of them on its own tells you a sheet is good. A buyer who specifies all three, and then confirms them on a physical sample, controls the cloth. A buyer who quotes only a thread count is easy to mislead.

This guide is for anyone writing a specification for woven bed linen: sheeting, duvet covers, pillowcases and shams. It explains what each number does, where each one is abused, and which one to lean on for which fabric.

What each number actually measures

Start by separating the three, because they are routinely muddled in tender documents and on retail packaging.

Metric	What it measures	Unit	Higher number means
GSM	Mass of cloth per unit area	Grams per square metre	Heavier, denser cloth
Thread count	Threads per square inch, warp plus weft	Count per square inch	More threads packed in, if counted honestly
Yarn count	Fineness of the yarn	Ne, Nm, Lea or denier or dtex	Finer yarn, on the indirect systems

The trap is treating them as interchangeable. A high thread count made from thick, cheap yarn can weigh the same as a lower count in a finer yarn, and feel worse. GSM and thread count are results; yarn count is one of the inputs that produces them.

GSM: weight per square metre

GSM, grams per square metre, is the most honest single number on the list because it is hard to fake. You cut a known area, weigh it, and divide. It reflects how much fibre is actually in the cloth, taking in the yarn thickness, the number of threads and the weave together.

For heavier and textured goods, GSM is usually the better control than thread count. Linen, linen-cotton blends, matelassé, waffle and flannelette are specified by weight because thread count says little about them. A crisp linen sheet and a soft one can share a thread count and differ sharply in GSM.

The limit of GSM is that it does not describe the hand or the construction. Two cloths at the same GSM can feel completely different depending on the weave, the finish and the yarn. So GSM is a floor you set to stop a supplier thinning the cloth, not a full description of it. Because the exact weight that suits a product depends on the fibre, the weave and the market, ask your supplier what GSM they run for the construction you want, and lock it against a sample rather than to a number in isolation.

Thread count: threads per square inch, and why it is gamed

Thread count is the number of threads in a square inch of cloth, counting the warp and the weft together. A genuine 200 thread count percale, made from single-ply yarns, is a sound, breathable, durable sheet. The problem is not the metric. It is the marketing that has been built on top of it.

The main abuse is ply counting. If a yarn is made of two thinner strands twisted together, an honest count treats it as one thread. Inflated counting treats it as two, so a real 300 count is advertised as 600, and a real 400 as 800 or more. The cloth is not finer or denser; the arithmetic is. Very high advertised counts, above roughly 600, almost always rest on this trick, on padding with extra filling picks, or on both.

There is also a physical ceiling. You can only pack so many threads of a given thickness into a square inch before the cloth stops breathing and starts to feel stiff and slick. Past that point a higher number buys you a worse sheet, not a better one. This is why experienced buyers treat a four-figure thread count as a warning rather than a selling point.

To specify thread count safely:

• State single-ply unless you have a reason not to. It removes the ply-count game at a stroke.
• Pair the count with a yarn count. A count means nothing without knowing the thickness of the thread making it.
• Name the weave. Percale and sateen at the same count feel different, one matte and cool, one smooth and lustrous.

Yarn count: the number under both

Yarn count measures how fine the yarn is, and it sits underneath GSM and thread count alike. It is the input that decides how fine and how light a cloth can be.

The systems trip people up because some run backwards. On indirect systems, a higher number means a finer yarn.

System	Used for	Direction
Ne, cotton count	Cotton and cotton blends	Higher is finer
Nm, metric count	Many staple yarns, including linen blends	Higher is finer
Lea	Linen	Higher is finer
Denier or dtex	Filament yarns such as tencel and viscose	Higher is heavier, coarser

So a 40s cotton (Ne 40) is finer than a 30s, and a fine sheeting yarn lets you build a higher honest thread count without the cloth turning boardy. On filament yarns the logic flips: denier and dtex are direct, so a bigger number is a heavier yarn. Getting the direction wrong is a common specification error, and it is worth writing the system name next to the number every time.

Which number matters for which fabric

You do not weight all three equally. Match the primary control to the cloth.

Fabric	Lead with	Also state
Cotton percale and sateen sheeting	Thread count, single-ply	Yarn count, weave
Linen and linen-cotton	GSM	Yarn count, weave
Matelassé, waffle, jacquard	GSM	Construction, repeat
Tencel and tencel blends	GSM	Yarn count in denier or dtex
Flannel and brushed goods	GSM	Fibre, finish

The pattern is simple. For fine cotton sheeting, thread count still carries useful information, as long as it is honest and paired with a yarn count. For anything heavier, textured or made from linen, GSM leads and thread count is close to meaningless.

How to specify without getting caught out

A clean cloth specification does not rest on one hero number. It gives a supplier enough to weave the exact fabric twice.

• Fibre and blend ratio, for example 100 percent linen, or 55 linen and 45 cotton.
• GSM, with a tolerance, usually plus or minus 5 percent.
• Weave, such as plain, percale, sateen, matelassé or waffle.
• Yarn count, with the system named, and single or two-ply stated.
• Thread count where the fabric warrants it, on an honest single-ply basis.
• Finish, such as stone washed, calendered or brushed.

Then, and this is the step that actually protects you, approve a physical sample against those figures before bulk. A counter sample woven to your specification, roughly a week on woven cloth, lets you check the GSM by weighing it and confirm the hand, rather than trusting a number on a page. A vertically integrated mill with its own looms can weave to a stated GSM and yarn count and put a swatch in your hand to prove it. See the woven capabilities for the constructions available, and private label for how sampling and minimums work.

If two suppliers quote very different thread counts for what looks like the same sheet, ask each for the yarn count and the ply, and weigh the samples. The GSM usually tells you which quote is real.

Common questions

Is a higher thread count always better?

No. Beyond roughly 400 on single-ply cotton, more threads make a sheet denser and less breathable rather than better, and most very high counts are inflated by counting plied yarns as separate threads. A genuine 200 to 400 single-ply percale or sateen outperforms an advertised 1000. Ask for the yarn count and whether the number is single or multi-ply.

Should I specify GSM or thread count?

It depends on the fabric. For fine cotton sheeting, an honest thread count paired with a yarn count is useful. For linen, blends, matelassé, waffle and any textured or heavier cloth, GSM is the more reliable control and thread count tells you little. When in doubt, specify GSM, because it is measured by weighing and is hard to fake.

What does the yarn count tell me that thread count does not?

Yarn count tells you how fine the thread is, which thread count alone hides. A high count in thick yarn and a lower count in fine yarn are different cloths. Naming the yarn count, and its system, stops a supplier meeting your thread count with coarse yarn and a heavier, cheaper sheet.

How do I check a supplier is meeting the spec?

Weigh a sample of known area to verify the GSM, then check the yarn count and ply against what was quoted. Approve a counter sample woven to your written specification before bulk, and keep a sealed reference. If you need help setting tolerances, get in touch with your fibre, weave and target weight.