GSM (grams per square metre) is the weight of one square metre of fabric. It is one of the first checks on every knit and woven fabric, from greige inspection to the final finished-fabric report. Use the free calculator below to get GSM from a round cutter sample, any sample size, or a full roll, and check it against the required GSM in one step.
GSM Calculator
Calculate fabric GSM (grams per square metre) from a cutter sample, any sample size, or a full roll.
Standard GSM cutter = 100 cm². GSM = weight (g) × 100.
GSM = weight (g) ÷ (length × width in cm²) × 10,000.
GSM = weight (g) ÷ (length (m) × width (m)). Tubular fabric has two layers, so width is doubled.
Compare with required GSM (optional)
How to use the GSM calculator
- Round cutter: cut a sample with a GSM cutter, weigh it on a precision balance, and enter the weight in grams. The standard cutter area is 100 cm², so 1.80 g gives 180 GSM.
- Any sample size: if you don’t have a cutter, cut an accurate square or rectangle, measure length and width in cm, and enter the weight.
- Full roll: enter the roll weight (kg), length (m) and width (cm). Choose Tubular for tube fabric, because a tube has two layers and the width is doubled.
- Compare (optional): enter the required GSM and tolerance to see straight away whether the fabric passes.
GSM formulas
| Method | Formula | Example |
|---|---|---|
| Round cutter (100 cm²) | GSM = sample weight (g) × 100 | 1.80 g × 100 = 180 GSM |
| Any sample size | GSM = weight (g) ÷ (length × width in cm²) × 10,000 | 7.20 g ÷ (20 × 20) × 10,000 = 180 GSM |
| Full roll, open width | GSM = weight (g) ÷ (length (m) × width (m)) | 25,000 g ÷ (90 × 1.80) = 154.3 GSM |
| Full roll, tubular | GSM = weight (g) ÷ (length (m) × width (m) × 2) | 25,000 g ÷ (90 × 0.90 × 2) = 154.3 GSM |
How to test GSM correctly
- Condition the fabric first. Fabric straight from the stenter or dryer is warm and dry and weighs light. Let it relax and reach room conditions before cutting.
- Take several samples across the width. Cut from both edges and the middle, keeping away from the selvedge, and use the average.
- Lay the fabric flat and relaxed. Don’t stretch knit fabric while cutting, or the GSM will read low.
- Use a sharp cutter and a calibrated balance. A blunt blade leaves loose fibres and uneven edges; the balance should read to at least 0.01 g.
GSM tolerance
Most buyers accept a GSM tolerance of about ±5% on finished fabric, but always follow the buyer’s own requirement. For a 180 GSM order at ±5%, the acceptable range is 171–189 GSM.
Frequently asked questions
What does GSM mean in fabric?
GSM stands for grams per square metre. It tells you how heavy the fabric is: a light single jersey may be around 120–160 GSM, while fleece is often 280–350 GSM.
Why is the round cutter weight multiplied by 100?
A standard GSM cutter cuts exactly 100 cm². One square metre is 10,000 cm², which is 100 times larger, so the sample weight × 100 gives grams per square metre.
Why does GSM change after dyeing and finishing?
Knit fabric shrinks and relaxes in wet processing, and the stenter and compactor then set the final width and length. Over-feeding or under-feeding, the set width, and how much the fabric is compacted all change the finished GSM.