GSM Explained: How Fabric Weight Affects Garments

GSM means grams per square metre — the weight of one square metre of fabric. It's the single most useful number for predicting how a cloth will feel, drape and wear, and it's the first figure most sourcing managers scan on a spec sheet.

How GSM is measured

The standard method is charmingly simple: a circular GSM cutter punches a disc of exactly 100 cm² from the fabric, the disc goes on a precision balance, and the reading in grams is multiplied by 100. Cut from several places across the width, average the results, and you have the fabric's GSM.

If a supplier quotes in ounces per square yard — common for denim and canvas — convert with 1 oz/yd² ≈ 33.9 GSM. So a 12 oz denim is roughly 407 GSM.

Rough GSM guide by end use

GSM range	Typical use
60–110	Voile, lawn, fine shirting, linings
110–160	Poplin, cambric, everyday shirting
160–220	Twill, light bottomweights, dresses
220–320	Chinos, workwear, heavier bottomweights
320+	Canvas, denim, outerwear, bags

These are guides, not rules — weave and finish shift the feel too. Knits run on their own scale: single jersey tees commonly sit around 140–180 GSM, heavier interlock and fleece well above that.

What weight changes in the garment

GSM touches almost every property a wearer notices:

• Drape — lighter cloth flows and gathers; heavier cloth holds structure and silhouette
• Opacity — below roughly 110 GSM, whites and pale shades in plain weaves can turn sheer; check over a contrast surface
• Durability — more grams per square metre generally means more fibre absorbing abrasion
• Comfort and climate — a 130 GSM poplin and a 240 GSM twill suit very different seasons and markets
• Cost — weight is fibre, and fibre is money; GSM is a large driver of price per metre

GSM vs construction

GSM and construction work together. A tight construction in fine yarns can still be lightweight; a loose weave in coarse yarns can be heavier than it looks. Use GSM for a quick read, then confirm with construction and a physical swatch — two 150 GSM fabrics can behave completely differently if one is a dense poplin and the other an open-sett sheeting.

Finishing moves the number

The GSM on a greige spec is not the GSM you'll cut. Preparation and finishing cause the cloth to shrink and consolidate, which usually raises finished GSM, while heavy washes or brushing change the hand without necessarily changing the weight much. Standard commercial practice allows a tolerance of around ±5% on nominal GSM — write that tolerance into your order so everyone measures against the same rule.

Specifying GSM in a brief

If you have a target weight, say so — "cotton twill around 240 GSM, peached." It lets us match candidates fast and develop to your exact hand-feel. If you don't have a number, send a reference swatch or even a garment: weighing it is a five-minute job, and it anchors the whole development.

State the target, the tolerance you'll accept, and whether the figure is greige or finished. Those three details prevent most weight disputes before they start.

Filter our Fabric Library by construction, request free swatches to feel the weight yourself, or start a development with a target GSM.