The single most common reason a sewing project disappoints is fabric weight. The color was right, the fiber was right, but the finished garment hangs limp or stands up like cardboard. Weight is what determines that, and it is the easiest spec to check before you buy.
What GSM actually means
GSM stands for grams per square meter. Take a piece of the fabric one meter by one meter and weigh it. That number is the GSM. Higher GSM means more fiber packed into the same area, which means a heavier, denser, more opaque cloth.
American mills often quote ounces per square yard instead. The two measure the same thing. To convert roughly, multiply ounces by 34 to get GSM, or divide GSM by 34 to get ounces. A 12 oz fleece is about 400 GSM.
One warning: denim is sometimes quoted in ounces per running yard rather than per square yard, which is why a 14 oz denim and a 14 oz fleece do not feel equally heavy. When in doubt, ask for the GSM.
Weight chart by project
T-shirts and tops
140 to 180 GSM. Light enough to drape, heavy enough not to be transparent. Below 140 you are into sheer territory, which is lovely for a drapey blouse and frustrating for a basic tee. Above 200 the shirt starts to feel structured rather than soft.
Hoodies and sweatshirts
280 to 450 GSM. This is the range people ask about most. Around 280 to 320 GSM gives you a lightweight sweatshirt good for spring layering. 350 to 400 GSM is the classic hoodie weight, substantial without being stiff. Above 450 GSM you are in heavyweight territory, the kind of fleece that feels expensive and takes real effort to sew.
Jeans and jackets
300 to 475 GSM (roughly 10 to 14 oz). Midweight denim around 10 to 12 oz is the everyday jeans range and behaves on a home machine. Above 14 oz you need a heavy-duty needle, a walking foot helps, and the fabric will break in over months rather than weeks.
Dresses and blouses
100 to 180 GSM. Drape matters more than body here. Tencel, rayon, silk, and lightweight linen live in this range. If a fabric feels too stiff in your hand, it will look stiff on the body.
Upholstery and bags
400 GSM and up. Canvas, heavy twill, and upholstery-weight linen. Durability outranks drape completely.
Weight is not the whole story
Two fabrics at identical GSM can behave completely differently. A 200 GSM linen is crisp and structured. A 200 GSM rayon jersey pools like liquid. Fiber determines drape; weight determines body. You need both to predict how something will hang.
Construction matters too. A loosely knit 250 GSM sweater knit feels airy. A densely woven 250 GSM twill feels solid. Same weight, opposite hand.
How to check before you commit
Every listing at APC Fabrics states the weight in GSM, ounces, or both. If you are between two options, order a swatch or a single yard first. One yard is a cheap way to avoid buying eight yards of something that turns out wrong for the project.
When you are ready, browse by what you are making: jersey knits for tees, fleece and french terry for sweats, or denim for jeans and jackets. Everything is sold by the yard and cut to order as one continuous piece.