Lesson 1 · Fabric basics
GSM — how heavy is a fabric?
5 min
In a real company
Fabric merchandiser, fabric QA / store in-charge, sourcing executive
Buyers specify fabric by GSM (grams per square metre). Every fabric lot that arrives is checked against it — a lighter fabric means the mill short-supplied, a heavier one changes your consumption and cost.
Key ideas
- GSM = weight in grams of 1 square metre of fabric.
- In the lab a round GSM cutter cuts exactly 100 cm²; weight × 100 = GSM.
- Light: below 100 (voiles) · Medium: 100–200 (shirts, T-shirts) · Heavy: 300+ (denim, fleece).
- oz/yd² is the US unit: GSM × 0.029494.
Formula
- Sample area (m²)
- = Length (m) × Width (m)
- GSM
- = Sample weight (g) ÷ Sample area (m²)
- oz/yd²
- = GSM × 0.029494
Worked example
QA cuts a 10 × 10 cm swatch from an incoming jersey roll. It weighs 1.85 g.
- 1Area = 0.1 m × 0.1 m = 0.01 m²
- 2GSM = 1.85 ÷ 0.01 = 185 g/m²
- 3In oz: 185 × 0.029494 = 5.46 oz/yd²
✅ 185 GSM — check it against the buyer's spec (e.g. 180 ± 5%).
Try it live in the calculatorCommon mistakes
- Weighing the swatch while it is damp — always condition it first.
- Cutting an uneven swatch by hand; use the GSM cutter.
- Comparing greige GSM with finished GSM — dyeing and finishing change the weight.
Quick quiz
Answer 2 of 3 correctly to complete the lesson.
1. A 100 cm² swatch weighs 2.2 g. What is the GSM?
2. Which GSM is typical for a basic T-shirt?
3. 10 cm × 10 cm equals how many m²?