Weight in grams, what the number tells you

Short answer: Grams per square metre describes how much fabric there is per unit of area. The number tells you about thickness and body, but nothing about quality.

What the number covers

Grams per square metre, often written as gsm, tells you how much one square metre of the fabric weighs. A fabric of 150 grams is thin, 250 grams is medium, and 350 grams is thick sweat fabric. The number gives you a quick idea of whether a garment is light and airy or heavy and full, see bamboo joggers for women.

How it is measured

A piece of fabric with a known area is cut out and weighed. The weight is then converted to a full square metre. The method is the same for all fabrics, so the number can be compared across products and shops. It is measured on the fabric itself before sewing, so it says nothing about cut or size.

Thickness is not quality

A thin fabric made from good yarn lasts longer than a thick fabric made from poor yarn. The weight only shows how much material there is, not how well it is spun or knitted. A heavy fabric can easily be made from short fibres that pill quickly. So never choose on the highest number alone, see bamboo jogging suit.

What the number says about warmth

A higher number usually means a thicker fabric that holds warmth better. A fabric around 350 grams suits cold days and clothes you relax in at home during winter. A fabric of 150 grams is better for summer or as an inner layer under a jumper. The medium weight covers most other days of the year.

What the number says about drape

Weight also affects how clothing hangs on the body. A light fabric falls softly and follows the lines of the body closely. A heavy fabric stands out a little more and gives a calmer, fuller silhouette. For a top that should sit lightly, a low number is often right. For a sweatshirt with more structure, a higher number fits better.

What the number is good for

It is the best way to compare two products when you cannot touch them. When shopping online, you can use the number to see whether a jumper is thinner or thicker than one you already own. Check the weight of a garment you know and like, and use it as a reference point, see the range for women.

What the number does not tell you

The number says nothing about the fibre surface, whether the yarn is fine or coarse, or whether the knit is loose or tight. Two fabrics with the same weight can therefore feel very different. One may be soft and supple, the other stiff and rough. Use the weight as one of several points, and also read what the garment is made from.

Choose by use

Think about when and how you will wear the clothes. A jogging suit for the sofa in winter can happily be heavy. A top for warm days or for wearing under a blouse should be light. If you choose by use rather than by the biggest number, you get clothes that suit the day and get worn often.

Frequently asked questions

What does grams per square metre mean

How much fabric there is in one square metre. A higher number means a thicker and usually warmer fabric, while a low number means a light fabric.

Is a high number better

Not necessarily. It means thicker, not better. For a summer t-shirt, a low number is often the right choice.

Where do you find the number

In the product description, often as gsm or grams per square metre. All serious shops state it.