You've seen "380gsm heavyweight hoodie" in a product description and wondered what it actually means for the feel and quality of the garment. GSM, grams per square metre, is the single most important fabric specification you'll encounter as a clothing brand, and understanding it will change how you design and source your products.
What Does GSM Mean?
GSM stands for grams per square metre. It measures how much one square metre of a fabric weighs in grams, which tells you its density and thickness. The higher the GSM, the heavier and denser the fabric and generally, the more substantial and premium the garment feels in hand.
GSM is a universal measurement that applies to all fabric types: jersey, fleece, French terry, denim, canvas, and more. It's not about fibre composition, it's purely about density. A 300gsm cotton-polyester blend and a 300gsm pure cotton fabric can feel very different, even though their GSM is the same.
GSM Ranges Explained
Lightweight: 100–180 GSM
Lightweight fabrics are breathable, drapey, and ideal for warm-weather and performance garments. They're comfortable against the skin but won't offer warmth or structural weight. Think summer tees, running tops, and performance underlayers.
Best for: Summer t-shirts, athletic tops, mesh sportswear, linings
Medium Weight: 180–280 GSM
The most versatile GSM range. Fabrics here have enough body to hold structure without feeling heavy. This is the standard weight for everyday t-shirts (180–220gsm) and mid-weight hoodies (240–280gsm). A reliable, commercial sweet spot.
Best for: Everyday t-shirts, long sleeves, lightweight hoodies, basic sweatshirts
Heavyweight: 280–380 GSM
Heavyweight fabrics are where premium streetwear lives. A 340gsm hoodie has a dense, substantial hand feel that signals quality before the customer even looks at the label. These fabrics hold their shape through repeated washing and photograph with a rich, full appearance.
Best for: Premium hoodies, heavyweight crewnecks, coach jackets, quality sweatpants
Ultra-Heavyweight: 380+ GSM
Ultra-heavyweight fabrics are reserved for the most premium streetwear and workwear. A 420gsm hoodie is a deliberate statement, noticeably thick, structured, and substantial. These fabrics cost more to produce and require careful construction but deliver an unmatched premium feel.
Best for: Luxury streetwear, high-end workwear, statement outerwear
GSM Reference Table by Garment Type
| Garment | Typical GSM Range | Recommended GSM |
|---|---|---|
| Basic t-shirt | 140–200 gsm | 160–180 gsm |
| Premium t-shirt | 200–260 gsm | 220–240 gsm |
| Lightweight hoodie | 220–300 gsm | 260–280 gsm |
| Midweight hoodie | 280–360 gsm | 300–340 gsm |
| Premium heavyweight hoodie | 360–450 gsm | 380–420 gsm |
| Crewneck sweatshirt | 260–380 gsm | 300–340 gsm |
| Tracksuit bottoms | 260–380 gsm | 300–360 gsm |
| Performance jersey | 120–180 gsm | 140–160 gsm |
| Denim jeans | 280–400 gsm | 320–360 gsm |
GSM to oz/yd² Conversion
American mills and US-based brands usually quote fabric weight in ounces per square yard (oz/yd²) instead of GSM. The conversion is fixed: 1 oz/yd² = 33.9 gsm. To convert ounces to GSM, multiply by 33.9; to go the other way, divide.
| oz/yd² | GSM (approx.) | Typical use |
|---|---|---|
| 4.0 oz | 136 gsm | Lightweight summer tee |
| 5.3 oz | 180 gsm | Standard everyday t-shirt |
| 6.5 oz | 220 gsm | Premium heavyweight tee |
| 8.5 oz | 288 gsm | Midweight hoodie / crewneck |
| 10 oz | 339 gsm | Heavyweight hoodie |
| 12 oz | 407 gsm | Ultra-heavy streetwear fleece |
| 14 oz | 475 gsm | Raw / selvedge denim |
If a supplier quotes you "a 10oz hoodie," you now know that's roughly a 340gsm garment, squarely in premium heavyweight territory.
How GSM Is Measured
Factories measure GSM with a circular fabric cutter and a precision scale. The cutter punches out a sample of exactly 100 square centimetres; that swatch is weighed in grams, and the result is multiplied by 100 to give grams per square metre. It takes seconds and is accurate to within a few grams.
You can approximate it at home without a cutter: weigh a finished garment on kitchen scales, then compare like for like. A standard adult large t-shirt uses roughly 1.5–1.8 square metres of fabric, so a tee that weighs 300g is in the neighbourhood of 170–200gsm once you allow for seams, collar and hems. It's rough, but it's enough to tell a lightweight tee from a heavyweight one when comparing samples.
When you order a sample, ask for the measured GSM to be confirmed on the spec sheet rather than relying on the catalogue figure. Knit fabrics can vary by ±5% between dye lots, and washing can change the effective weight as fibres relax and shrink.
How GSM Affects Cost, Printing and Shipping
GSM isn't just a feel decision. It moves three numbers in your budget:
- Fabric cost: fabric is bought by the kilogram, so a 400gsm hoodie simply contains roughly one third more raw material than a 300gsm one cut to the same pattern. Heavier always costs more, before any quality difference.
- Decoration behaviour: heavier, denser fabrics carry embroidery beautifully because the stitching has a stable base and won't pucker. Very light fabrics (under ~160gsm) can distort under dense embroidery and usually suit screen print or DTF instead.
- Shipping weight: couriers charge by weight and volume. A carton of fifty 420gsm hoodies weighs noticeably more than the same carton at 300gsm, which matters on air freight. Factor this in when comparing per-unit quotes that include delivery.
Choosing GSM by Season
A simple planning rule most brands follow: spring/summer drops sit at the light end of each garment's range, autumn/winter drops at the heavy end. A brand running a year-round core hoodie often picks a middle weight (around 320–350gsm) that works in most climates, then reserves 400gsm+ for a winter capsule. If your customers are spread across hot and cold regions, the mid-weight compromise usually outsells either extreme.
Higher GSM Doesn't Always Mean Better
This is one of the most common misconceptions in fashion manufacturing. GSM should match the garment's intended use and seasonal positioning, not simply be as high as possible.
A 420gsm French terry hoodie is perfect for a premium winter streetwear collection. That same fabric in a performance running top would be wrong, too heavy, too hot, and too restrictive for movement. Context always matters.
Additionally, within the same GSM, quality varies enormously based on fibre quality and spinning method. A 280gsm ring-spun cotton t-shirt will feel significantly better than a 280gsm open-end spun equivalent at the same weight. GSM is one variable among several.
Always Specify GSM and Construction Together
GSM tells your manufacturer the weight, but not the fabric structure. Always pair your GSM with the construction type:
- Single jersey: smooth face, slightly textured back. Standard for t-shirts.
- French terry: smooth face, looped back. Premium sweatshirts and hoodies.
- Brushed fleece: smooth face, soft brushed back. Warm, popular in mid-range hoodies.
- Ribbed jersey: stretchy and structured. Used in cuffs, waistbands, and ribbed garments.
A complete fabric specification looks like this: "350gsm brushed-back French terry, 80% cotton 20% polyester." That gives your manufacturer everything they need to source or match the correct material. Add it to your tech pack alongside your measurements and Pantone references.
GSM FAQs
What GSM is best for a premium hoodie?
Most premium streetwear hoodies sit between 380 and 420gsm. That range gives the dense, structured feel buyers associate with quality while still being wearable indoors. If you want a year-round hoodie rather than a winter statement piece, 320–350gsm is the safer commercial choice.
What GSM should a good t-shirt be?
An everyday retail t-shirt is typically 160–180gsm. Premium and oversized streetwear tees run heavier, usually 220–240gsm, which drapes with more structure and feels noticeably more substantial. Below 140gsm, tees start to feel like promotional giveaways.
Is a higher GSM always better quality?
No. GSM measures weight, not quality. Fibre grade, spinning method (ring-spun vs open-end), and knit construction affect how a fabric feels and lasts at least as much as its weight. The right GSM is the one that matches the garment's use, season, and price point.
How do I convert GSM to ounces?
Divide the GSM by 33.9 to get oz/yd². For example, 340gsm ÷ 33.9 ≈ 10oz. To convert ounces to GSM, multiply by 33.9.
Does GSM change after washing?
Effective GSM can rise slightly after the first wash because cotton fibres relax and the fabric shrinks, concentrating the same weight into a smaller area. This is why production-accurate samples should be washed once before you approve fit and hand feel.
Still unsure which weight suits your product? Send us your idea through a quote request or order a sample in your target GSM — comparing a 300gsm and a 400gsm swatch in hand answers the question faster than any guide.
