GSM is the single number most people use to judge fabric, and on its own it predicts almost nothing. This guide explains what it actually measures, what it cannot tell you, and the weights that suit hoodies, T-shirts and sweatshirts.
What GSM means
GSM stands for grams per square metre: the weight of a piece of fabric cut one metre by one metre. A 180 GSM jersey means a square metre of it weighs 180 grams.
That is all it is. It is a measure of mass per area — not thickness, not quality, not warmth, not durability. Every other property people attribute to GSM is inferred, and the inference is often wrong.
The American equivalent is ounces per square yard, usually written oz/yd² or just “oz”. A 6 oz T-shirt and a 203 GSM T-shirt are the same thing.
| oz/yd² | GSM (approx.) | Typically |
|---|---|---|
| 3.5 oz | 119 | Lightweight, semi-sheer tee |
| 4.5 oz | 153 | Standard summer T-shirt |
| 5.3 oz | 180 | The common mid-weight tee |
| 6.0 oz | 203 | Heavier tee, light sweatshirt |
| 7.5 oz | 254 | Light hoodie or sweatshirt |
| 9.5 oz | 322 | Standard hoodie weight |
| 12 oz | 407 | Heavyweight hoodie |
To convert: multiply oz/yd² by 33.9 to get GSM, or divide GSM by 33.9 to go the other way.
What GSM genuinely predicts
Three things follow fairly reliably from a higher GSM, all else being equal:
- Cost. More fibre per metre means more material, and fabric is usually the largest single cost in a garment.
- Opacity. Heavier fabric shows less through. This is why cheap white tees look see-through and heavier ones do not.
- Drape. Light fabric falls close to the body; heavy fabric holds its own shape. That is why oversized streetwear is cut in heavy cloth — the weight is what makes it hang that way.
Notice that warmth is not on that list.
What GSM cannot tell you
It does not tell you how warm the garment is
Warmth comes from trapped air, not from mass. A 280 GSM brushed fleece is warmer than a 280 GSM French terry at exactly the same weight, because brushing raises a pile that holds air against the skin. Our hoodie fabric guide explains the difference between the two constructions. The terry’s loops are left flat, so they hold less.
If you only remember one thing from this page: construction decides warmth, GSM only scales it.
It does not tell you how good the fabric is
Two fabrics at 320 GSM can be made from completely different yarn. Ring-spun cotton, where the fibres are twisted into a smooth continuous yarn, feels softer and pills less than open-end carded cotton of the same weight. Combed cotton goes further, removing the shortest fibres before spinning.
A heavy garment in poor yarn will look worse after ten washes than a lighter garment in good yarn. Weight is not workmanship.
It does not tell you how dense the knit is
The same weight of yarn can be knitted tightly or loosely. A tight knit at 180 GSM is more durable, more opaque and prints more crisply than a loose knit at the same number. A loose knit is airier and sometimes more comfortable in heat.
There is no way to tell these apart from the specification. You have to handle the fabric, or trust the supplier.
It does not tell you what happens after washing
An untreated cotton garment can lose several percent of its dimensions on a first hot wash, which changes its GSM as the fabric contracts and thickens. Pre-shrunk or enzyme-washed fabric is far more stable. A GSM measured before finishing — on greige fabric — can differ noticeably from what you receive.
Always ask whether a quoted GSM is finished or greige.
GSM by garment
These are the bands each garment is commonly made in. Treat them as orientation, not as a standard — mills knit outside them routinely.
T-shirts
| GSM | Feel | Suits |
|---|---|---|
| 120–150 | Light, drapes, can show through in white | Hot climates, fashion fits, layering |
| 150–180 | The common everyday tee | General use, printed merchandise |
| 180–220 | Substantial, opaque, holds shape | Premium tees, workwear, frequent washing |
| 220+ | Heavy, structured, boxy | Streetwear, heavyweight fashion pieces |
Sweatshirts and hoodies
| GSM | Feel | Suits |
|---|---|---|
| 200–250 | Light layer, closer to a heavy tee | Warm climates, spring and autumn, layering |
| 250–320 | The standard hoodie and sweatshirt weight | Year-round everyday wear |
| 320–400 | Substantial, warm, holds its shape | Cold weather, workwear, premium streetwear |
| 400+ | Heavy, structured, slow to dry | Outdoor use, statement heavyweight pieces |
Sports jerseys
| GSM | Feel | Suits |
|---|---|---|
| 130–160 | Very light, fast drying | Hot-weather match kit, running |
| 160–200 | The usual jersey weight | Most team sports, training kit |
| 200–240 | More structured, more durable | Contact sports, heavy-use training wear |
Jerseys sit lighter than casualwear for a reason: in sport, a fabric that holds sweat and heat is a liability, so weight is kept down and the fibre does the work.
How to use GSM when you are ordering
A GSM figure on its own is not a specification. Four things turn it into one.
| Specify | Why it matters | Example |
|---|---|---|
| Weight | Cost, opacity, drape | 320 GSM, finished |
| Construction | Warmth and surface | Brushed fleece, not French terry |
| Composition | Shrinkage, print method, feel | 80% cotton, 20% polyester |
| Yarn | Softness, pilling, print crispness | Ring-spun, 30s count |
“320 GSM” tells a supplier almost nothing, and the fabric you choose also decides which printing methods are available to you. “320 GSM finished brushed fleece, 80/20 cotton-poly, ring-spun, pre-shrunk” tells them exactly what to quote, and gives you something to hold them to when the goods arrive.
How to check a GSM claim yourself
If a supplier quotes a weight and you want to verify it, you can measure it with a ruler and a kitchen scale accurate to a gram. It takes two minutes and settles the question.
- Cut a square of fabric from a seam allowance or an offcut — 10 cm by 10 cm is enough. Be accurate; a millimetre out at this size is a one percent error.
- Weigh it in grams.
- Multiply by 100. A 10 cm square is one hundredth of a square metre, so a 3.2 g square is 320 GSM.
Two cautions. Measure the fabric dry and at room humidity — cotton absorbs moisture from the air, and a damp sample reads heavy. And cut from the body of the garment, not a ribbed cuff, waistband or seam, which are made from different fabric.
For a production order, a mill will supply a cutting and a test report. For a sample you have in your hand, the kitchen scale is enough to tell 320 GSM from 250.
Frequently asked questions
Is higher GSM always better?
No. Higher GSM means more fabric, which costs more and takes longer to dry. For a summer T-shirt or a match jersey, lower is better. Higher is better only when you want warmth, opacity or structure.
What GSM is a good T-shirt?
150 to 180 GSM covers most everyday T-shirts. 180 to 220 feels noticeably more substantial and survives washing better. Below 140 the fabric starts to show through in pale colours.
What GSM is a good hoodie?
280 to 320 GSM for year-round wear. 350 and above for genuinely cold weather. Below 250 is a light layer rather than a warm one.
How do I convert GSM to oz?
Divide GSM by 33.9. So 180 GSM is about 5.3 oz, and 320 GSM is about 9.5 oz.
Does higher GSM mean the fabric lasts longer?
Not by itself. Yarn quality and knit density matter more. A tightly knitted 180 GSM fabric in ring-spun cotton will usually outlast a loosely knitted 220 GSM fabric in coarse yarn.
Why does the same GSM feel different on two garments?
Because GSM says nothing about construction, yarn or finishing. A brushed fabric feels warmer and softer than a smooth one at the same weight, and ring-spun yarn feels better than carded at any weight.
Is GSM measured before or after finishing?
It can be either, which is why it is worth asking. Finishing processes such as washing, brushing and pre-shrinking change the weight, so a greige figure can differ from the fabric you actually receive.
Next: T-shirt fabric guide — cotton, blends, GSM and knits explained.
Weight is only half the story on a hoodie — the knit matters too: fleece vs French terry.