What GSM Means on a Sweatshirt, and What Weight to Buy

GSM stands for grams per square metre. It is the weight of one square metre of the fabric, and on a sweatshirt or hoodie it is the quickest way to tell a thin layer from a substantial one. Higher number, heavier and denser fabric. That is the short answer. The rest of this page is about what the number does and does not tell you, so you can buy the right weight for how you actually wear it.

What GSM actually measures

Cut a one-metre square of the fabric, weigh it, and that is the GSM. It says nothing about colour, fit or print. It tells you how much material is there.

You will also see ounces per square yard, usually on American labels. The conversion is fixed: one oz/yd² is about 33.9 gsm. So 12 oz is roughly 406 gsm, and 8.5 oz is roughly 288 gsm. If a listing gives only one of the two, you can work out the other with a calculator.

Two things to keep in mind. First, the number is for the fabric, not the finished garment, so a larger size of the same sweatshirt weighs more but has the same GSM. Second, not every seller publishes it. If a product page is vague about weight, that is worth noticing.

The rough weight bands

There is no official standard for what counts as light or heavy. These are the bands most people in clothing work with, and they are a guide rather than a rule.

  • Under about 250 gsm. Lightweight. Good for layering or warmer days. Drapes softly and packs small.
  • About 250 to 350 gsm. Midweight. The everyday range for most hoodies and sweatshirts. Works on its own or under a jacket.
  • Above about 350 gsm. Heavyweight. Stiffer when new, holds a boxier shape, and feels noticeably substantial in the hand.

T-shirts sit lower on the scale. Around 150 gsm is a standard tee. Anything over about 200 gsm starts to feel like a heavyweight shirt.

Weight is not the whole story

Two sweatshirts at the same GSM can feel very different. Three things account for most of it.

Fibre. All-cotton fleece and cotton-polyester blends behave differently. Neither is automatically better. The label tells you the split, so check it rather than guessing.

Knit and finish. A brushed interior feels softer and warmer than an unbrushed one at the same weight. A cotton face means the outer surface is cotton while the inside is a blend, which gives a clean surface for printing or embroidery.

Construction. Side seams, ribbed cuffs and hem, a ribbed collar and double-needle stitching all change how a garment sits and how it wears over time. These details are usually listed, and they matter as much as the weight.

So use GSM to narrow the field, then read the rest of the label.

How to choose the weight for you

Start with how you will wear it, not with the biggest number.

  • If you run warm, or it goes under a coat, a midweight around 280 to 300 gsm is usually enough. A heavyweight under a winter coat can feel bulky.
  • If it is your outer layer for most of the year, heavyweight earns its place. It keeps its shape and does the job without anything over it.
  • If you want a structured, boxy look, weight helps. Heavier fleece stands away from the body. Lighter fleece follows it.
  • If you want something soft from day one, a brushed midweight will feel better on the first wear than a stiff heavyweight.

And check the fit description alongside the weight. A relaxed-fit heavyweight and a modern-fit midweight are different garments, even before the numbers come in.

What Belfer makes, by weight

For reference, here are the published fabric weights for our adult sweatshirts and hoodies, taken from each product page.

Some colourways use a different blend or weight. The product page lists the exceptions, so check the one you are buying.

If you want the heavy end, the 406 gsm pieces are the ones. If you want an everyday layer, the 275 to 288 gsm range covers it. You can see the full range in men's streetwear and women's streetwear.

The number on the label is not the point. How the thing wears in a year is. GSM is simply the first honest clue.

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