Fabric GSM Explained: What the Number Means
Fabric GSM stands for grams per square metre: the weight of one square metre of fabric. A 200 GSM jersey weighs 200 grams for every square metre of cloth. Because the unit measures weight per area, it is independent of fabric width and roll length, which makes it the standard way to compare fabrics and to write a specification. Higher GSM generally means a heavier, thicker and more substantial fabric, and lower GSM means lighter and thinner.
GSM is useful but incomplete. It tells you nothing about fibre, yarn quality or structure, so a 180 GSM combed cotton jersey and a 180 GSM open-end jersey can feel and wear very differently. Treat fabric GSM as one line of a specification rather than a quality guarantee.
How to Calculate Fabric GSM
The calculation is simple: GSM equals the weight of a fabric sample in grams divided by its area in square metres. The easiest sample is a circle of exactly 100 square centimetres, which is one hundredth of a square metre. The weight in grams multiplied by 100 is then the GSM. Textile labs use a round GSM cutter for this and a precision scale that reads to two decimal places.
A 100 square centimetre sample weighs 1.85 grams. Multiply by 100 and the fabric is 185 GSM. In imperial units that is 185 divided by 33.9, about 5.5 ounces per square yard. If the same fabric comes on a roll 150 cm wide, one metre of that roll weighs about 185 times 1.5, or roughly 278 grams.
That last figure shows why GSM and fabric consumption are different things. GSM describes the cloth. How much cloth a garment uses depends on the pattern, the fit and the roll width, and it is the combination of the two that drives fabric cost.
GSM to oz/yd² Conversion
Some suppliers, especially denim and workwear mills, quote weight in ounces per square yard. The conversion is fixed: one ounce per square yard is about 33.9 GSM. The table gives the values most buyers need, rounded to one decimal place.
Fabric GSM and ounces per square yard
| GSM | oz/yd² (approx.) | Typical context |
|---|---|---|
| 120 | 3.5 | Very light jersey, summer tees |
| 150 | 4.4 | Lightweight t-shirt jersey |
| 180 | 5.3 | Standard t-shirt, mid-weight polo |
| 200 | 5.9 | Mid-weight tee, light French terry |
| 240 | 7.1 | Heavyweight tee, light sweatshirt |
| 280 | 8.3 | Midweight hoodie fleece, light denim |
| 320 | 9.4 | Heavier hoodie fleece |
| 400 | 11.8 | Heavyweight hoodie, mid-weight denim |
Conversions use 1 oz/yd² = 33.9 GSM and are rounded. The context column is typical, not a rule.
Denim is often described by its ounce weight, for example 12 oz, which is roughly 407 GSM. If a supplier quotes ounces, convert before comparing it with a GSM figure from another mill.
Light, Mid and Heavyweight: Fabric GSM by Garment
There is no industry-wide definition of lightweight, midweight or heavyweight, and the labels shift with the garment: a heavyweight t-shirt is lighter than a lightweight hoodie. The table gives the bands most factories and brands use as a working guide. Use it to sanity-check a quote, not to replace a reference garment.
Typical fabric GSM bands by garment
| Garment | Lightweight | Midweight | Heavyweight |
|---|---|---|---|
| T-shirt (single jersey) | 120–150 | 160–200 | 210–300 |
| Polo shirt (piqué) | 160–180 | 180–220 | 230–280 |
| Sweatshirt | 220–260 | 260–320 | 320–380 |
| Hoodie | 200–260 | 270–340 | 350–450 |
| Joggers | 200–260 | 260–340 | 350–420 |
| Jeans (denim) | 270–340 (8–10 oz) | 340–410 (10–12 oz) | 410–540 (12–16 oz) |
Working bands in GSM. They are typical and vary by product, market and factory. Always confirm against a reference garment.
The bands overlap on purpose. A boxy streetwear tee often sits at the top of the t-shirt range for structure, a topic we cover in our boxy and oversized t-shirt guide.
Typical Fabric GSM Ranges at a Glance
The chart below shows the same information visually, one bar per garment, so you can see how the categories overlap. It is a quick way to check whether a weight you have been quoted is plausible for the product.
Typical GSM ranges by garment type
Typical ranges, grams per square metre
Typical ranges. They vary by product, factory and fabric. Use as a plausibility check, not a specification.
Notice how hoodies and joggers span a wide band. That is because they can be made in French terry for spring or in thick brushed fleece for winter. The right figure depends on season and look as much as the garment name.
T-Shirt GSM: Choosing the Right Weight
T-shirt GSM has the most influence on how a tee looks and feels. Light weights in the 120–150 range drape closely and feel cool but can look thin once washed. Mid weights, roughly 160–200, are the standard retail tee and balance softness, opacity and cost. Heavier tees, from about 210 upward, hold their shape, hang with structure and give the boxy silhouette that streetwear favours.
Yarn quality matters as much as the number. A combed ring-spun jersey at 180 GSM usually feels smoother and wears better than an open-end jersey at the same weight, which we explain in our guide to ring-spun vs combed cotton. When you compare tees, check GSM, yarn type and finish together.
Hoodie GSM: Midweight, Heavyweight and the Fleece Question
For hoodies, fabric GSM is also a statement about warmth and market position. Lighter weights around 200–260 suit spring wear and layering, midweights from about 270 to 340 are the mainstream choice, and heavyweights above 350 carry the premium streetwear look. Fleece and French terry at the same GSM do not feel the same, because fleece has a brushed back that adds loft and warmth.
When you specify a hoodie, state the GSM of the finished fabric, the structure and the blend together. Our hoodie fabric guide compares French terry and fleece in detail, and fleece fabric has its own guide to types and weights.
How to Measure Fabric GSM from a Swatch
You can check a swatch or a finished garment panel yourself with inexpensive equipment, which is useful when a sample looks lighter or heavier than the specification. The steps below follow the common method used in textile labs.
Measuring fabric GSM in five steps
- 1PrepareLay the fabric flat and relaxed, away from seams, hems and printed areas.
- 2CutUse a 100 square centimetre GSM cutter, or cut a 10 cm by 10 cm square.
- 3WeighWeigh the sample on a scale accurate to 0.01 g and record the grams.
- 4CalculateMultiply the weight in grams by 100 to get GSM.
- 5RepeatTake three samples from different places and average them.
A square cut by hand is less precise than a round cutter. For specifications that matter, ask the factory for a lab figure.
Measure the fabric in the condition you care about. Greige fabric before dyeing and finishing, finished fabric, and fabric after washing all have different GSM, because processing and shrinkage change the density. State which one you mean.
GSM Tolerance and Common Mistakes
No mill produces fabric at exactly the stated weight. A commonly quoted tolerance is around plus or minus 5 per cent, so a 200 GSM fabric might legitimately measure anywhere between about 190 and 210. Some factories and fabric types allow more or less, so agree the figure in writing. A tight tolerance is worth asking for if you are matching a reference or a previous batch.
Specify fabric GSM properly
- State GSM for the finished fabric, not a nominal weight.
- Agree the tolerance and the test method with the factory.
- Write the fibre, yarn type, structure and finish next to the GSM.
- Say whether the figure is before or after washing.
- Check the bulk fabric GSM against the approved sample, not a catalogue.
- Do not compare GSM between fabrics of different structure without touching them.
A common mistake is to chase a high number as a mark of quality. A heavier fabric made from poor yarn can feel coarse and pill sooner than a lighter one made from good yarn, so judge by handfeel and tests as well. Our garment testing guide lists the checks to request.
What Fabric GSM Changes: Drape, Cost, Shipping, Shrinkage
Weight has knock-on effects well beyond feel. Heavier fabric uses more yarn, so cost rises, and freight is often charged by weight or volume, so heavier garments cost more to ship. Heavier knits tend to have more structure and less drape, while lighter fabrics move and cling. The table summarises the main effects.
How heavier and lighter fabric GSM compare
| Factor | Heavier GSM | Lighter GSM |
|---|---|---|
| Drape and shape | More structure; holds a boxy or tailored shape | Softer drape; clings and flows more |
| Warmth | Warmer, more insulating | Cooler, more breathable |
| Material cost | More yarn per metre, so usually higher | Less yarn per metre, so usually lower |
| Shipping weight | Heavier cartons; freight cost can rise | Lighter cartons |
| Opacity | Less see-through, especially in light colours | More see-through, especially in white |
| Sewing and printing | Thicker seams; prints sit well but feel heavier | Easier to sew flat; thin fabric may show print through |
| Shrinkage | Depends on structure and finishing, not weight alone | Depends on structure and finishing, not weight alone |
General tendencies. Shrinkage is driven by yarn, structure and finishing more than by GSM, so always test the exact fabric.
Because of these links, it pays to decide fabric GSM before you finalise price targets, not after. Changing the weight later changes the cost, the freight and the look all at once.
How Ruhrose Approaches Fabric GSM
Ruhrose develops hoodies, jersey garments, denim and woven casualwear for UK buyers, with production in Bangladesh. We start from your reference garment or target feel, measure its fabric GSM, propose options at one or two weights, and sample before bulk, so the weight is agreed in writing and checked against the sample. We do not quote weights in advance without seeing the product. For the full approach, read about our sampling process.