GSM — grams per square metre — is the primary quality and specification metric for knit fabrics in Bangladesh's garment industry. It determines how much a fabric costs per kilogram, how it will behave in washing, and whether it meets the buyer's quality standard. Getting the GSM right from the start of sourcing saves enormous problems at inspection.
The GSM Formula
To calculate the GSM of a fabric sample, you need a circular cutter (standard 100 cm² sample size) and a precision scale accurate to 0.01 grams. If you do not have a circular cutter, you can cut any known area and convert.
GSM = (Sample weight in grams / Sample area in cm²) × 10,000 Using standard 100 cm² circular cutter: GSM = Weight of sample (g) × 100 (Multiply weight in grams by 100 directly) Example: Sample cut with 100 cm² cutter weighs 1.85 grams GSM = 1.85 × 100 = 185 GSM For a non-standard sample (e.g., 10cm × 15cm = 150 cm²): GSM = (2.90 grams / 150 cm²) × 10,000 = 193 GSM
Common GSM Ranges by Fabric Type
Knowing typical GSM ranges helps you verify whether a fabric is appropriate for the intended end use — and whether the supplier's declared GSM is plausible.
Typical GSM Ranges by Fabric Type
| Fabric Type | Typical GSM Range | Common Use |
|---|---|---|
| Single jersey (lightweight) | 120 – 150 GSM | Summer t-shirts, inner layers |
| Single jersey (standard) | 160 – 190 GSM | Most t-shirts, polos |
| Single jersey (heavyweight) | 200 – 240 GSM | Premium t-shirts, casual wear |
| Pique / lacoste | 170 – 220 GSM | Polo shirts |
| Fleece (inner face) | 200 – 280 GSM | Sweatshirts, hoodies |
| Rib (1×1 or 2×2) | 180 – 250 GSM | Cuffs, collars, hemlines |
| French terry | 220 – 280 GSM | Sweatpants, casual tops |
| Interlock | 160 – 220 GSM | Leggings, activewear, intimate |
Why GSM Accuracy Matters for Costing
Fabric in Bangladesh is sold and costed by kilogram, not by metre. A 5 GSM difference in a fabric that costs USD 3.50/kg seems trivial — but over a 100,000-piece order consuming 1.8 kg of fabric per piece, a 5 GSM under-specification means the supplier delivers 176 kg instead of 180 kg per 100 pieces: a real cost difference of USD 140 per 100 pieces, or USD 1,400 per 1,000 pieces across the order.
Note
Always condition fabric samples for 24 hours in standard atmospheric conditions (65% RH, 20°C) before testing GSM if you need results that match lab reports. Fabric absorbs moisture from the air, which adds weight. A sample tested immediately after unpacking will give a different GSM than one conditioned overnight.
Tip
When receiving fabric from a supplier, cut GSM samples from at least 5 different positions across the roll width and at both roll ends. GSM variation within a roll can be 5–10 GSM — if the centre is on-spec but the edges are 10 GSM lighter, the average will pass but the garments cut from the edges will be visibly thinner.