Three systems rise, three fall
Every yarn count answers the same question — how heavy is this yarn for its length — but two families answer it from opposite ends, and nothing in the numbers themselves tells you which family you are looking at.
A direct system states mass per unit length. Tex is grams per 1000 metres; denier is grams per 9000 metres. Thicker yarn, bigger number.
An indirect system states length per unit mass. The metric count Nm is metres per gram; the cotton count Ne is 840-yard hanks per pound. Thicker yarn, smaller number.
One yarn, getting steadily thicker, in all six systems| Tex | Denier | dtex | Nm | Ne | Typical use |
|---|
| 5 | 45 | 50 | 200 | 118 | Fine filament, hosiery |
|---|
| 15 | 135 | 150 | 67 | 39 | Shirting |
|---|
| 30 | 270 | 300 | 33 | 20 | Apparel, sheeting |
|---|
| 85 | 765 | 850 | 12 | 7 | Denim warp |
|---|
| 200 | 1800 | 2000 | 5 | 3 | Carpet, webbing |
|---|
Read the columns downward. The first three grow by a factor of forty; the last two shrink by the same factor. That is the whole difference, and it produces a specific confusion: a 30 denier is finer than a 70 denier, but a Ne 30 is coarser than a Ne 70. Same pair of numbers, opposite meanings, in two mills that both call it “the count”.
The calculator marks the direction with an arrow beside each system for exactly this reason. If a spec sheet gives a bare number and a unit you do not recognise, the direction is the first thing to establish, before the arithmetic.
Why denier does not convert to GSM
This is the most-searched conversion in textiles, and it does not exist.
A yarn count measures linear density — mass per unit of length, grams per kilometre. A fabric weight measures areal density — mass per unit of area, grams per square metre. They are different physical quantities, in the way that a speed and a distance are different quantities. No constant relates them.
What stands between them is the fabric’s construction, and it takes at least this much to cross the gap:
- Ends and picks per centimetre. How many warp yarns and how many weft yarns occupy each centimetre of cloth. A count says nothing about this, and it is the dominant term.
- Two counts, not one. Warp and weft are usually different yarns, often deliberately so — denim is the obvious case, with a heavier indigo warp against a lighter weft.
- Crimp. Yarn does not lie straight in cloth; it waves over and under the yarns crossing it, so more than a centimetre of yarn goes into each centimetre of fabric. How much more depends on the weave and on the relative tensions during weaving.
- Structure. A plain weave, a twill and a jersey knit built from identical yarn at identical density arrive at different weights and very different thicknesses.
- Finishing. Sanforising, brushing, coating, calendering and mercerising all change the finished mass per square metre after the cloth exists.
A converter that offers “denier to GSM” has silently assumed values for all of the above — that is, it has invented a fabric and is reporting its weight. The number it returns is real for that imagined cloth and wrong for yours. This page keeps the two panels separate and says so between them.
If you genuinely need to estimate a fabric weight from yarns, the route is a construction calculation: the total yarn length per square metre in each direction, multiplied by each yarn’s linear density, plus a crimp allowance and a finishing allowance. That is a mill calculation with several inputs, not a unit conversion, and it lands within a few percent at best.
The ounce that means two things
“Twelve ounce denim” is ambiguous, and the ambiguity is worth about forty percent.
Ounces per square yard is an areal density — the honest measure, directly comparable to GSM. Ounces per linear yard is the weight of one yard cut off the bolt, whatever width that bolt happens to be. Both get abbreviated to “oz”.
The same cloth, quoted per linear yard at different bolt widths| Bolt width | Square yards per linear yard | A 10 oz/yd² cloth quotes as | Overstatement |
|---|
| 36″ | 1.00 | 10.0 oz | none |
|---|
| 44″ | 1.22 | 12.2 oz | 22% |
|---|
| 54″ | 1.50 | 15.0 oz | 50% |
|---|
| 60″ | 1.67 | 16.7 oz | 67% |
|---|
| 108″ | 3.00 | 30.0 oz | 200% |
|---|
The factor is just the width over 36 inches, because a linear yard is 36 inches long by however wide the bolt is. At 36 inches the two figures coincide exactly — which is why the confusion has survived so long. On a 36-inch bolt, everybody is right.
Read the other way: a fabric offered at 12 oz per linear yard on a 60-inch bolt is 7.2 oz per square yard, or 244 g/m². That is a mid-weight twill, not the heavy denim that “12 oz” suggests to anyone who has bought jeans. The difference is a whole class of cloth.
The practical rule: if a quote is in ounces and no width is stated, the figure is not yet a specification. Ask which it is. GSM is not ambiguous in this way, which is a large part of why the rest of the world settled on it.
What each system is used for, and where
Nobody chose this. Each system survives in the trade that adopted it first, and a supply chain routinely crosses three of them between fibre and garment.
Where each count system is still the working unit| System | Direction | Where you meet it |
|---|
| Tex | Direct | The ISO unit. Technical textiles, sewing thread, industrial yarn, and most academic and standards work everywhere. |
|---|
| Decitex | Direct | Synthetic filament across Europe and Asia — polyester, nylon, viscose. Finer resolution than tex without decimals. |
|---|
| Denier | Direct | US practice and consumer-facing specifications worldwide: hosiery, ripstop, ballistic nylon, backpack fabric. |
|---|
| Metric (Nm) | Indirect | Wool and worsted through continental Europe; also common for handknitting yarn, where it appears as a fraction like 2/28. |
|---|
| Cotton (Ne) | Indirect | Cotton spinning in the UK, the US, India, Pakistan and Bangladesh. The “40s” on a shirt label, and the working unit of the world’s largest cotton mills. |
|---|
| Worsted | Indirect | Worsted wool, mostly British. Uses a 560-yard hank rather than cotton’s 840, so a worsted count and a cotton count of the same number are different yarns. |
|---|
For fabric weight the split is simpler and cleaner. GSM is used almost everywhere — across Europe, India, China and Bangladesh, and by most technical buyers in the US and UK too. Ounces per square yard persists in US retail and in the denim and canvas trades on both sides of the Atlantic, where “14 oz” carries meaning that “475 gsm” does not.
A common sourcing case runs the full gauntlet: an Indian mill quotes the yarn in Ne, the fabric in GSM and the width in inches; a European brand specifies in tex and centimetres; and the US buyer at the end wants ounces. All three are describing the same cloth.
Reading a real spec sheet
A woven fabric specification usually looks something like this, and every field is doing work:
100% cotton · 16s × 12s · 108 × 56 · 3/1 twill · 320 gsm · 58/60″
- 16s × 12s — the warp and weft counts in Ne. Two different yarns, the warp finer than the weft. In tex those are 36.9 and 49.2, and note that the smaller Ne is the heavier yarn.
- 108 × 56 — ends and picks per inch: the thread density that, with the counts, produces the weight.
- 3/1 twill — the weave. It sets the crimp, and therefore how much yarn is consumed per square metre.
- 320 gsm — the finished areal weight. About 9.4 oz/yd².
- 58/60″ — the width, given as a range because looms and finishing do not hold width exactly. It is also what any per-linear-yard figure would depend on.
Two things to check before treating any of it as fixed. First, whether the weight quoted is greige or finished — unfinished cloth straight off the loom weighs less than the same cloth after finishing, and considerably less than after a first wash and shrink. Second, whether the test was made at standard conditions: textiles hold moisture, and cotton at 65% relative humidity carries several percent more mass than the same cotton bone-dry. A mill certificate and a warehouse scale disagreeing by three percent is usually humidity, not fraud.
None of that is a reason to distrust the arithmetic. The conversions on this page are exact — the tex-to-denier factor of nine is a definition, and the 33.906 g/m² per oz/yd² comes from an exact yard and an exact ounce. The variability is in the cloth, not in the conversion.
Sources and methodology
The tex system and the direct-versus-indirect distinction are standardised, so those are settled by the ISO and ASTM references. The 590.5 constant behind the cotton count is not a measured figure at all — it falls out of the 840-yard hank and the avoirdupois pound, both exact, which is why the NIST reference sits alongside them.