Fabric GSM Calculator

GSM — grams per square metre — is the single number that decides how a knit fabric feels in the hand, how opaque it is on the body, and what it costs per kilo. Two jerseys made from the same yarn at 160 GSM and 220 GSM are not variations of one product; they are two different products aimed at two different seasons. This page gives you the calculator, the mill method behind it, and the tolerances that matter when you are placing an order.

What GSM Tells You — and What It Does Not

GSM is mass per unit area. That is all it is. It says nothing about fibre content, yarn quality, shrinkage, or colour fastness. A 200 GSM fabric made from combed compact yarn and a 200 GSM fabric made from carded open-end yarn weigh the same and behave very differently after ten washes. Treat GSM as the starting point of a specification, never the whole specification.

What GSM does predict reliably is hand feel and opacity within one construction. Move a single jersey from 150 to 200 GSM and it stops being a summer layer and starts behaving like a year-round tee. Move brushed-back fleece from 280 to 380 GSM and you move from a light sweatshirt to a winter hoodie.

How GSM Is Measured Inside a Mill

The standard method is a circular cutting die. The die stamps out exactly 100 cm² of fabric, which is 0.01 m², so the arithmetic collapses to something you can do in your head:

GSM = swatch weight in grams × 100

If your die has a different area, the general form is GSM = weight (g) × 10000 ÷ area (cm²), which is what the calculator above uses.

One reading is not a measurement. Knit fabric is rarely uniform across the width — the two edges of a roll are often knitted at slightly different tension than the centre. We cut five samples across the full width (left edge, quarter, centre, three-quarter, right edge), weigh each one, and record both the average and the spread. If the spread between highest and lowest exceeds about 5 percent, the roll gets flagged for re-checking before it goes into cutting.

Why Your Number and the Mill Number May Not Match

Moisture is the usual culprit. Cotton and viscose are hygroscopic; a roll stored in a humid Guangdong warehouse in July can weigh 3 to 5 percent more than the identical roll measured in a dry winter room. Conditioning samples for 24 hours at 20 °C and 65 percent relative humidity removes most of that difference, which is why lab reports state conditioning alongside the result.

The second culprit is finishing. Brushing, enzyme washing, singeing and compacting all change GSM after the fabric leaves the knitting machine. A greige fabric knitted at 190 GSM can finish at 205 GSM after brushing raises the surface, or drop below 185 after an aggressive enzyme wash removes surface fibre. Always state whether you are specifying greige GSM or finished GSM — this single ambiguity causes more disputes than almost anything else in knit sourcing.

GSM and Ounces per Square Yard

Buyers in the United States still quote weight in ounces per square yard. The conversion constant is 33.9057:

GSM = oz/yd² × 33.9057

So 4.5 oz is about 152 GSM, 5 oz is about 170 GSM, and 7 oz is about 237 GSM. The calculator gives both figures side by side so you can reply to either convention without doing mental arithmetic mid-negotiation.

Turning GSM Into the Numbers You Actually Buy

GSM is a laboratory quantity. Purchasing happens in kilograms and metres, so you need two more steps:

• Weight per linear metre (g/m) = GSM × width in metres. A 200 GSM fabric at 1.85 m usable width weighs 370 g per running metre.
• Weight per linear yard = g/m × 0.9144.
• Roll or order weight (kg) = g/m × length in metres ÷ 1000.

This is also how freight is estimated. A 1000 m order of 200 GSM fabric at 1.85 m width is roughly 370 kg of fabric before packaging — enough to decide whether you are shipping a pallet or a container.

Typical GSM Ranges by End Use

Tolerance: Why 200 GSM Is Never Exactly 200

A commercial tolerance of plus or minus 5 percent is normal for knitted fabric. Holding plus or minus 3 percent is achievable on single jersey when yarn lot, machine gauge and stitch length are controlled and the roll is finished on a compactor, but it costs more and it should be written into the contract rather than assumed.

Judge a supplier less on whether they hit the exact number and more on whether they hit the same number every time. Consistency between rolls matters far more in cutting than a one-off perfect reading, because a roll that is 4 percent light next to a roll that is 4 percent heavy will produce garments that fit differently after washing.