What is gsm or oz in fabric? All about fabric weight.

Think of fabric weight as how thick a fabric is. Fabric weight can affect ease of construction, wearing comfort and drape - ie how the final garment "hangs".

When first started sewing I was always browsing fabrics online. Hitting the sort button: "Sort by lowest price".

This summer I came across this beautiful cotton-elastane twill for £5 a metre! I love a mildly stretchy woven fabric and it is just so comfortable to wear. I planned to turn this into a summer dress. When it arrived... it was too thick for the hot and beautiful British summer!

Grasping the concept of the fabric weight will help you choose the correct fabric for your project. And doesn't it sound cool when you rock up in a fabric shop and go: "I'd like a cotton poplin, approximately 130-150gsm in weight"?

5 things to know about fabric weight

1. Fabric weight is measured in grams per square metre, gsm.

2. Fabric weight is affected by the type of fibres used. For instance, linen is heavier than silk. And cotton is heavier than viscose and so on.

3. How "densely" fibres are spun into threads will affect the fabric weight. For example, cotton canvas are made from thicker cotton threads than a cotton poplin.

4. Next, how densely threads are woven or knitted into a fabric? A cotton canvas can come in different weight. The easiest to imagine this is your bed linen. A lower quality 200-thread cotton is more loosely woven than a fine 400-thread cotton percale. And think about how "sheer" these compare to each other!

5. Finally, the finishing of the fabric also affects its weight. How is it dyed? Is the fabric backed by crepe? Is the cotton waxed?

What is the fabric weight for my fabric?

As a rule of thumb, majority of silks you can buy tend to be light weight. Most dressmaking or suiting cottons, linens and wools are medium. With coating, canvas and upholstery fabrics being the heaviest.

This lovely diagram from Collette sums up fabric weight quite succinctly.