This page teaches a buyer, merchandiser or factory planner how to convert a fabric's weight between GSM (grams per square metre) and oz/yd2 (ounces per square yard), so that two fabrics quoted in different units can be compared on equal terms. It is for anyone who reads a fabric quote, a tech pack line, or a spec sheet, and no previous lesson is required, though it reuses Order A's and Order B's own already-fixed knit and denim weights from earlier lessons. This mainly teaches the information flow: turning one fabric weight, stated in one unit, into the other unit, so both sides of a comparison mean the same thing.
At work, a buyer cannot compare a knit fabric in GSM against a woven fabric in oz/yd2 by looking at the two numbers side by side. The units are not directly comparable until one is converted into the other. Without this skill, a buyer reads "6.5 oz" next to "180 GSM" and guesses which is heavier, based only on which number looks bigger, when the two numbers do not even measure the same scale. A wrong guess here is not a small slip: it can lead a buyer to accept a fabric heavier or lighter than the product actually needs, discovered only once the goods are already cut or shipped.
You need: Order A's fixed fabric weight, 180 GSM, and Order B's fixed fabric weight, 12 oz denim, both already stated in section 7 of the curriculum rules. No previous lesson is required, though Lesson 3.1 (calculating fabric consumption) is useful background.
By the end of this lesson you can:
Not covered here: how a fabric's usable width changes a marker (Lesson 3.3), calculating an order's total fabric requirement (Lesson 3.4), and calculating fabric cost from that total (Lesson 3.5).
| Term | Meaning |
|---|---|
| GSM | Grams per square metre: the standard way fabric weight is stated. |
| Oz/yd2 (ounces per square yard) | A fabric-weight unit common for woven fabrics, especially denim, stating how many ounces one square yard of the fabric weighs. |
| Knit fabric | Fabric made by looping yarn, usually sold, cut and weighed in GSM. |
| Woven fabric | Fabric made by crossing warp and weft yarns; denim, a common woven fabric, is often weighed in oz/yd2 instead of GSM. |
| Denim | A woven cotton fabric, usually in a twill weave, commonly used for jeans and often quoted by weight in ounces per square yard. |
| GSM to oz/yd2 conversion | The standard textile-unit conversion oz/yd2 = GSM / 33.9, used to compare a knit fabric's weight, usually stated in GSM, with a woven fabric's weight, often stated in oz/yd2. |
Knit fabrics are typically weighed in GSM, grams per square metre. Woven fabrics, especially denim, are often weighed in oz/yd2, ounces per square yard, instead. Both units measure the same physical property, how heavy a fixed area of fabric is, but on two different numeric scales, so a number in one unit cannot be read as if it were already in the other. The standard conversion is a fixed formula: oz/yd2 = GSM / 33.9, and, run the other way, GSM = oz/yd2 x 33.9. This is a universal textile-industry conversion, not specific to this academy's own orders. Order A's own fabric is already fixed at 180 GSM; Order B's own denim is already fixed at 12 oz. Converting each into the other unit lets a buyer or mill compare two fabrics quoted in different units on equal terms.
| What can differ | The shapes you will meet | Why it matters |
|---|---|---|
| GSM (knit fabrics) | The usual unit for knit fabric, including Order A's own 180 GSM single jersey. | A knitting mill such as Rowad Knits states weight in GSM by default. |
| Oz/yd2 (woven fabrics, especially denim) | The usual unit for many woven fabrics, including Order B's own 12 oz denim. | A denim mill such as Suez Denim states weight in ounces by default, not GSM. |
| A mixed-unit comparison | A buyer comparing a "200 GSM" knit quote against a "6 oz" woven quote. | Without converting both to the same unit first, a buyer cannot tell which fabric is actually heavier. |
| The calculator's live formula | Both conversions, GSM to oz/yd2 and oz/yd2 to GSM, are single-step formulas on this course's fabric calculator. | A buyer or planner never needs to compute the formula by hand at work; the calculator does it live. |
| Knit-to-garment, terry and home textiles | These product families also mix GSM and oz/yd2 depending on whether the fabric is knitted or woven. | The conversion formula is not specific to T-shirts or jeans; it applies to any fabric weight, in any product family. |
Neither unit is used everywhere across the trade: a buyer converts between them whenever a fabric quote arrives in a unit different from the one already used for comparison.
The case we followSara, the buyer at Northline Apparel, is sourcing a new woven fabric for an export, Make to Order product and receives a quote stating the fabric's weight as "6.5 oz". She wants to check this new fabric's weight against Order A's own 180 GSM knit fabric, the fabric she already knows well from Northline's basic T-shirt. Sara cannot compare "6.5" against "180" directly, since the two numbers are stated in different units. She needs to convert one figure into the other unit before she can tell which fabric is actually heavier.
The worked numberOrder A's fabric is already fixed at 180 GSM (docs/02 section 7). Applying the standard formula:
Order B's denim is already fixed at 12 oz (docs/02 section 7). Applying the standard formula in the other direction:
No new fabric has been chosen in either case; only the number describing an already-fixed fabric has been converted into the other unit.
| Order | Original weight | Converted weight |
|---|---|---|
| Order A (knit) | 180 GSM | About 5.3 oz/yd2 |
| Order B (woven denim) | 12 oz/yd2 | About 407 GSM |
A common mistake is assuming a bigger number in one unit is automatically a heavier fabric than a smaller number in a different unit. A "6.5 oz" woven fabric looks smaller than "180 GSM" written next to it, so a buyer comparing the two numbers directly might assume the woven fabric is much lighter. Converting 6.5 oz/yd2 to GSM shows the opposite: 6.5 x 33.9 is about 220 GSM, heavier than Order A's own 180 GSM. The cost of skipping the conversion is discovered only once the wrong fabric weight has already been accepted for a product it does not suit.
Fabric weight can be written in two different units. Knit fabric is usually weighed in GSM, grams for every square metre. Woven fabric, especially denim, is often weighed in ounces for every square yard instead. Both units measure the same thing, how heavy the fabric is, but they use different scales, so the numbers themselves cannot be compared directly. A fixed calculation turns one into the other: divide the GSM number by 33.9 to get ounces per square yard, or multiply the ounces number by 33.9 to get GSM. Order A's own 180 GSM fabric comes out at about 5.3 ounces per square yard. Order B's own 12 ounce denim comes out at about 407 GSM. Comparing the raw numbers without converting first can make a heavier fabric look lighter, or the other way round.
Sara, the buyer at Northline Apparel, is reviewing a new woven fabric for a possible export order:
The document Sara reads, the supplier's quote line:
Is this new fabric heavier or lighter than Order A's 180 GSM knit fabric? Decide before you open the answer.
Heavier. Converting 6.5 oz/yd2 to GSM: 6.5 x 33.9 is about 220 GSM, which is heavier than Order A's own 180 GSM.
The two facts that decide this are the formula, GSM = oz/yd2 x 33.9, run in the direction needed because the quote arrived in ounces, and the value itself, 6.5 oz, taken directly from the supplier's quote line. The converted figure, about 220 GSM, is clearly above Order A's own 180 GSM.
Had Sara instead compared "6.5" against "180" directly, without converting, she would have wrongly assumed the new fabric was much lighter than Order A's, when it is actually heavier once both weights are expressed in the same unit.
This risk is framed qualitatively, since no specific order has actually been produced against the wrong fabric weight in this case. Comparing two fabric weights in different units without converting first risks choosing a fabric weight that does not suit a product's needs, too light or too heavy compared to what was actually intended. This mismatch is often discovered only once the fabric has already been ordered, cut, or shipped, by which point correcting it costs time and fabric already spent. Converting correctly, using the standard formula in the direction needed, is a small step that avoids a mismatch that is expensive precisely because it is caught late.
The Fabric calculator (this course's workbook) holds both conversions worked through in this lesson: GSM to oz/yd2 and oz/yd2 to GSM. Enter a fabric weight in the yellow input cell, and the white result cell applies the correct formula automatically, as a live formula.
| Question | Order A knit (filled in) | Order B denim (filled in) | Your fabric |
|---|---|---|---|
| Original unit | GSM | Oz/yd2 | |
| Original weight | 180 | 12 | |
| Formula applied | oz/yd2 = GSM / 33.9 | GSM = oz/yd2 x 33.9 | |
| Converted weight | About 5.3 oz/yd2 | About 407 GSM |
Download the Fabric calculator from the course page and fill in your own fabric's weight in the third column.
1. What is the standard formula to convert a fabric weight from GSM to oz/yd2?
2. Order A's fabric is fixed at 180 GSM. What is this fabric's approximate weight in oz/yd2?
3. A different woven fabric is quoted at 9 oz/yd2. Applying GSM = oz/yd2 x 33.9, approximately what GSM does this correspond to?
| EN | AR | FR | TR | Meaning |
|---|---|---|---|---|
| GSM | GSM | GSM | GSM | Grams per square metre: the standard way fabric weight is stated. |
| Oz/yd2 (ounces per square yard) | أونصة/ياردة مربعة | Once par yard carré (oz/yd2) | Yarda kare başına ons (oz/yd2) | A fabric-weight unit common for woven fabrics, especially denim, stating how many ounces one square yard of the fabric weighs. |
| Knit fabric | قماش تريكو | Tissu tricoté | Örme kumaş | Fabric made by looping yarn, usually sold, cut and weighed in GSM. |
| Woven fabric | قماش منسوج | Tissu chaîne et trame | Dokuma kumaş | Fabric made by crossing warp and weft yarns; denim, a common woven fabric, is often weighed in oz/yd2 instead of GSM. |
| Denim | قماش الدنيم | Denim | Denim kumaş | A woven cotton fabric, usually in a twill weave, commonly used for jeans and often quoted by weight in ounces per square yard. |
| GSM to oz/yd2 conversion | تحويل GSM إلى أونصة/ياردة مربعة | Conversion GSM vers once/yd2 | GSM'den oz/yd2'ye dönüşüm | The standard textile-unit conversion oz/yd2 = GSM / 33.9, used to compare a knit fabric's weight, usually stated in GSM, with a woven fabric's weight, often stated in oz/yd2. |
You can now convert a fabric's weight between GSM and oz/yd2, so a knit fabric and a woven fabric quoted in different units can be compared on the same scale. The next lesson looks at a different question: how a fabric's usable width, once selvedge and shrinkage allowances are removed, changes how many pieces a marker can fit. Back to the course map