How the calculation works
GSM is the weight of one square metre of fabric. The calculator divides the weight of your sample by its area:
GSM = sample weight in grams ÷ (length in cm × width in cm ÷ 10,000)
Example: a 10 cm × 10 cm sample weighing 1.8 g has an area of 0.01 m², so the fabric is 1.8 ÷ 0.01 = 180 GSM.
Getting an accurate reading
- Use a scale that reads to 0.01 g. Kitchen scales are not precise enough for small samples.
- Cut the sample square, on a flat surface, without stretching the fabric.
- A larger sample, such as 20 cm × 20 cm, reduces the effect of cutting errors.
- Measure three samples from different places and average them. Fabric weight varies across a roll.
The fabric GSM guide lists the weights normally used for each garment.
Common questions
What is a GSM cutter?
A round cutter that cuts a fabric sample of exactly 100 square centimetres. The sample weight in grams multiplied by 100 is the GSM.
Can I use inches?
Convert to centimetres first: one inch is 2.54 cm. The result is also shown in ounces per square yard.