Fabric Weight Explained: What GSM Tells You

GSM is grams per square metre: the mass of one square metre of cloth. It is the number mills weigh, and the fastest way to compare two fabrics built the same way. It is also the number most often misread, since weight alone says nothing about fibre, knit structure or how a garment will feel on a body.

What does GSM mean on a fabric spec sheet?

GSM stands for grams per square metre. It is mass per unit area: how many grams one square metre of the cloth weighs. Mills, testing labs and buying offices all quote it, and it is the most direct way to compare two fabrics of the same construction. A weight with no fabric name beside it is half a specification.

How do you convert GSM to ounces per square yard?

One ounce per square yard equals 33.906 grams per square metre. The figure follows from the unit definitions: one ounce is 28.3495 grams and one square yard is 0.836127 square metres. To go from GSM to ounces, divide by 33.906. To go from ounces to GSM, multiply by the same figure.

Three worked examples cover most conversations. A standard retail tee at 180 GSM is 5.31 oz/yd², a heavyweight brushed fleece at 400 GSM is 11.80 oz/yd², and a US sheet written at 8 oz/yd² is about 271 GSM. Rounding is the only trap: a sheet that rounds to one decimal moves a 180 GSM fabric between 5.3 and 5.4 oz/yd², so ask for GSM when a tolerance matters.

What can a GSM figure tell you before you touch the cloth?

Weight is a proxy for several things at once. It tells you roughly how much yarn went into a square metre, how much light the cloth will block, and how the finished garment is likely to hang. Heavyweight at 400–500 GSM is dense enough to hold a boxy silhouette. A 240 GSM French terry is the cloth for a hoodie worn in a warm climate.

Weight also shows up in price, twice over. Heavier cloth costs more per kilo, and it sews slower. Moving from 320 to 420 adds roughly 30–35% more fabric by weight.

What does a GSM figure leave out?

Weight says nothing about what the cloth is made of or how it was built. Thickness, stretch, opacity and hand feel depend on the fibre and the knit as much as on the number. Two fabrics at 220 GSM can sit at opposite ends of a product range; 220 GSM in nylon and 220 GSM in polyester are different fabrics that happen to weigh the same. Composition is its own trade, set out in our guide to fibre and blend choice.

The clearest case is the fleece family. French terry is a loopback knit: the face is smooth and the back carries unbroken loops of yarn. Brushed fleece is the same base cloth with those loops brushed until they stand up as a nap. One extra process, one identical weight, two different garments. The full comparison sits in fleece versus French terry.

What changes	French terry at 320 GSM	Brushed fleece at 320 GSM
Back surface	Unbroken yarn loops	Loops brushed into a raised nap
Warmth on the same base yarn	Lighter three-season layer	Warmer; the nap traps air
Bulk through the marker	Thinner cloth, less room per piece	Thicker cloth, more room per piece
Surface for decoration	Smooth face takes fine print detail	Nap carries fine detail differently
Band we run	240–320 gsm	320–420 gsm

320 GSM is where those two bands meet. Our French terry runs 240–320 gsm and our brushed fleece runs 320–420 gsm, so a 320 GSM target can be met in either family and will not produce the same hoodie. A weight on an enquiry is not the specification; the fabric name beside it is.

Which weights suit a hoodie, a tee or a legging?

Our hoodie range is held and sourced from 240–550 GSM, across French terry, brushed fleece, heavyweight fleece and cotton/poly blends. Inside that band the working split is French terry 240–320 gsm, brushed fleece 320–420 gsm, heavyweight fleece 400–500 gsm and poly-cotton performance fleece 280–360 gsm. The hoodie manufacturing page lists each band beside the fabric it comes from.

Garment or fabric	g/m²	oz/yd²	What the weight does
Tri-blend jersey tee	130–160	3.8–4.7	The lightest route; soft, drapey fashion fits
Yoga tanks and tops	140–180	4.1–5.3	Light and breathable for hot practice and layering
Golf polyester piqué	160–220	4.7–6.5	The workhorse range for performance golf polos
Standard retail tee	180–200	5.3–5.9	The weight most retail programmes sell
Seamless or bonded polo	180–260	5.3–7.7	Interlock and ponte knits for bonded construction
Classic piqué polo	200–260	5.9–7.7	Corporate, uniform and retail programmes
Nylon-spandex leggings	220–260	6.5–7.7	Dense and smooth; holds shape through a squat
Sculpting leggings	260–300	7.7–8.8	High-density double knit for compression
Loop-back French terry	250–300	7.4–8.8	Light, dry handle for year-round hoodies
Heavyweight brushed fleece	400–500	11.8–14.7	Boxy silhouettes that survive repeated washing

Read the table by end use rather than by size. Every band above matches the fabric tables on the t-shirt, hoodie and yoga wear pages. A higher number is not a better garment: a 140–160 GSM tri-blend tee is correct for a drapey fashion fit, while a boxy oversized tee needs 220–260 GSM to hold its shape.

How do you measure the GSM of a sample yourself?

Cut a square with clean edges, measure both sides in centimetres, and weigh the piece on a scale that reads to 0.01 g. Divide the weight by the area in square metres. A 20 cm × 20 cm piece covers 0.04 m², so 7.5 g on that piece works out to 187.5 GSM.

Three habits make the reading trustworthy. Cut the piece away from the selvedge, since the edge carries a different weight from the body of the cloth. Lay it flat and measure without stretching. Weigh the piece on its own rather than resting it on a cutting mat. The fabric GSM calculator runs the same check in a browser.

What tolerance should a fabric weight spec allow?

We work to ±5% of the specified GSM. Every roll is re-weighed on arrival against the agreed figure, and a roll outside that tolerance is rejected rather than cut. The check uses a circular cutter and a gram scale on the incoming cloth, not the mill’s certificate. A 320 gsm target therefore accepts 304 to 336 gsm.

The tolerance matters at sampling too. If bulk is cut from cloth lighter than the roll the sample was made from, the finished goods feel lighter than the sample you approved, and the gap is visible on the shelf even where it is not visible on a spec sheet.

How should you write fabric weight into an RFQ or tech pack?

Write composition and weight as a pair, then add the knit structure and the mill if you have one. Field three of the hoodie tech pack is fabric and GSM, and it asks for that list: composition, knit structure, target weight, named mill. A target GSM with no fabric family beside it leaves the factory buying against an adjective.

The enquiry that moves fastest names the style reference, the fabric weight and blend, the colours, the quantity per colour and the size range. If you only have a target weight and a description of the garment, send those; we come back with the fabric options we hold in that range and a sampling plan. The RFQ field guide lists every field worth including, and the knitwear tech pack template shows where each number goes.

What do buyers ask most about fabric weight?

Does a higher GSM always mean better quality?

No. Higher weight adds density, opacity and structure, but the right figure depends on the garment, the climate it is worn in and the silhouette it has to hold. A 140–160 GSM tri-blend tee is correct for a drapey fashion fit, while a boxy oversized tee needs 220–260 GSM to hold its shape. Weight also behaves differently by fibre.

What GSM should I choose for a heavyweight hoodie?

400–500 GSM is what the market calls heavyweight: dense enough to hold a boxy silhouette and to survive repeated washing without losing shape. 320–400 suits an all-season retail hoodie, and 240–320 French terry suits layering and warmer climates. Moving from 320 to 420 adds roughly 30–35% more fabric by weight and a slower sewing operation.

Can two fabrics at the same GSM feel different?

Yes, and often. GSM measures mass per area, not how the cloth is built; fibre, knit construction and finishing all change the hand feel at the same weight. Nylon-spandex at 220 GSM is dense, smooth and opaque, while polyester-spandex at the same weight needs roughly 230 to 240 GSM for comparable coverage. French terry and brushed fleece show the same effect.

How do I convert a tee weight from ounces to GSM?

Multiply the ounce figure by 33.906. A 4.5 oz/yd² tee is about 153 GSM, a 5.3 oz/yd² tee is about 180 GSM, and a 6.1 oz/yd² tee is about 207 GSM. If the spec sheet rounds to one decimal, the converted figure can drift by a few grams either way, so ask for GSM on anything tolerance-sensitive.

What tolerance applies to the weight of bulk cloth?

We hold ±5% of the specified GSM. Each roll is re-weighed when it arrives and any roll outside the tolerance is rejected before cutting, so the cloth that reaches the line matches the weight that was signed off. The figure is checked on the roll rather than on the mill’s paperwork, and the same rule applies at sampling.

What should I send with my first fabric enquiry?

Send the style reference, the fabric weight and blend together, the colours, the quantity per colour and the size range. If you only have a target weight and a description of the garment, that is enough to start. Sampling takes 3–7 working days from a confirmed design, and bulk runs 15–25 days after the sealed sample is approved.

SLSPOLO has made knits in Humen, Dongguan since 2009, on an 18,000+ m² site with 180+ staff and a monthly capacity of 150,000–200,000 pcs. Minimum order is 100 pcs per style per colour, and 200 where the style uses bonded or seam-sealed construction. The quality system is ISO 9001, with full inspection to AQL 2.5 before dispatch.