Two t-shirts, same cotton, same factory, same price band. One feels like something you would pay $40 for. The other feels like a conference giveaway.
The difference is usually one number on the spec sheet, and most people ordering their first production run either skip it or copy it from a competitor's website. That number is GSM.
Get it right and your sample arrives roughly as you imagined. Get it wrong and you have 2,000 pieces that are technically correct and commercially useless — too sheer, too stiff, too hot for the market you sell to. Here is what GSM measures, the practical ranges per garment, how it behaves differently in knits and wovens, and the trap that catches nearly everyone.
What GSM means
GSM stands for grams per square metre. Cut one square metre of fabric, weigh it, and that is the GSM. Its usefulness comes from being independent of fibre, construction and finish — you can compare a cotton jersey to a polyester fleece on the same scale.
You may also see fabric weight in oz/yd², especially from American mills and in denim. One oz/yd² is roughly 33.9 GSM, so a 12 oz denim is about 407 GSM and a 6 oz tee about 203 GSM.
What GSM does not tell you
GSM measures weight, not quality. A coarse 220 GSM jersey made from cheap open-end yarn will feel worse than a 160 GSM jersey made from long-staple combed cotton. Weight is a starting point, not a verdict.
- Yarn count — 20s, 30s, 40s. Higher numbers mean finer yarn and generally a smoother hand.
- Fibre and staple length — combed vs carded, ring-spun vs open-end. This is where premium feel actually lives.
- Construction — single jersey, interlock, French terry, piqué. Same weight, completely different behaviour.
- Finish — enzyme wash, peached, mercerised. Changes hand feel dramatically at identical GSM.
“Never write GSM in a tech pack alone. Write GSM plus construction plus yarn count plus fibre. That is a specification a mill can actually match.”
Weight ranges that work
| Weight class | GSM range | Feels like | Typical uses |
|---|---|---|---|
| Very light | 80–130 | Sheer, drapey, cool | Summer blouses, linings, athletic mesh |
| Light | 130–180 | Soft, breathable, some transparency | Warm-climate tees, vests, light shirting |
| Mid | 180–250 | Structured but not stiff; opaque | Everyday tees, polos, dresses, light sweats |
| Heavy | 250–350 | Substantial, holds shape | Hoodies, sweatshirts, heavy tees, jackets |
| Very heavy | 350+ | Rigid, durable, protective | Denim, canvas, outerwear, workwear |
Garment-by-garment defaults
- T-shirt — 180 GSM is the industry sweet spot: breathable enough for warm weather, opaque enough to wear alone. 140–160 for hot climates, 200–240 for a premium heavyweight.
- Polo shirt — 200–240 GSM piqué. Lower and the collar loses structure after a few washes.
- Sweatshirt or hoodie — 280–350 GSM French terry or brushed fleece; 320 is a reliable default.
- Woven shirt — 110–140 GSM poplin for a crisp dress shirt, 150–200 GSM twill or oxford for something more casual.
- Denim jeans — 320–370 GSM for a light summer jean, 400–440 GSM standard, 470+ GSM for raw and selvedge.
- Leggings and activewear — 220–280 GSM. Below about 200 GSM, squat opacity becomes a problem you hear about in reviews.
Knits and wovens behave differently
A knit is made of interlocking loops. It stretches, it drapes, and at a given weight it feels softer and more open, because loose knits carry more air between the yarns. A woven has yarns crossing at right angles in a fixed grid — denser at equal weight, and barely stretching unless elastane is added.
The practical consequence: 180 GSM is a normal t-shirt and a fairly heavy shirting fabric. Never carry a GSM number across from one construction to another without checking it against that category's own range. Wovens also introduce thread count and weave type as variables GSM cannot capture — a 130 GSM poplin and a 130 GSM voile are different products.
Heavier is not better
The most common mistake in first orders. "Premium" gets translated into "heavy," a 250 GSM tee gets specified, and then the reviews say it is hot, slow to dry and boxy. Weight should follow the use case.
- Climate — if you sell into a hot, humid market, a heavy tee is a returns problem. 140–180 GSM suits most warm-climate markets.
- Drape — flowing silhouettes need low GSM. A 240 GSM jersey will not drape, no matter how good the pattern is.
- Print method — heavy screen prints sit better on mid to heavy fabrics; fine DTG detail needs a smooth, high-yarn-count surface more than it needs weight.
- Cost — GSM is close to linear with fabric cost, and fabric is typically 50–65% of FOB. Going from 180 to 240 GSM can add 20–30% to your fabric bill.
Specifying GSM so it survives production
Three things to write into your tech pack. First, give a tolerance — ±5% is standard and reasonable. If you write "180 GSM" with no tolerance, you have not made a decision, you have made an argument for later.
Second, state whether the figure is pre- or post-finishing. Washing, brushing, compacting and dyeing all move the number; a fabric knitted at 170 GSM can finish at 185. Specify the finished GSM, because that is the fabric your customer touches.
Third, approve a physical swatch, not a number. Ask for lab swatches at your target weight, handle them, then approve one and reference it in the tech pack by code. Numbers do not communicate hand feel; the swatch does. On a first order, also request a shrinkage test — lighter knits generally shrink more, and shrinkage is a sizing problem disguised as a fabric problem.
Frequently asked questions
- What GSM is best for a t-shirt?
- 180 GSM for a standard everyday tee. Drop to 140–160 for hot climates or a lighter fashion fit; go to 200–240 for a heavyweight premium tee.
- Is higher GSM better quality?
- No. GSM measures weight only. Yarn count, fibre quality, spinning method and finishing determine quality. A well-made 160 GSM fabric beats a poor 220 GSM one.
- How do I convert GSM to oz/yd²?
- Divide GSM by 33.9. So 400 GSM is about 11.8 oz — a standard mid-weight denim.
- What GSM is a good hoodie?
- 280–350 GSM. Around 320 GSM brushed French terry gives a substantial feel without becoming uncomfortably warm for three-season wear.
- Does GSM affect price much?
- Yes. Fabric is usually the largest component of a garment's cost, and weight is close to proportional to fabric consumption. A 30% GSM increase is a meaningful cost increase.
- Will my fabric come out at exactly the GSM I specify?
- Rarely, and that is normal. Specify a ±5% tolerance and confirm whether the figure is measured before or after finishing.
- Does GSM change after washing?
- The fabric can compact slightly, and finishing processes shift the figure. Always work from finished, post-wash GSM when specifying.
Fabric GSM is the fastest way to communicate how a garment will feel, but it is a starting point rather than a specification on its own. Pair it with construction, yarn count and fibre, give a ±5% tolerance, and approve a physical swatch before bulk fabric is booked. Choose weight for your climate and silhouette, not for a vague idea of premium.
Send us your target hand feel — or a garment you like — and we will match swatches at the right weight before anything is costed.