Fabric GSM Calculator

What GSM tells you

GSM is grams per square metre: what one square metre of a fabric weighs. It describes how heavy the fabric is regardless of its width or roll length, so it is the number buyers, weavers and processors use to agree on a quality and to cost it. It says nothing about the yarn or the weave, so two fabrics of the same GSM can look and feel quite different.

Formula 1: GSM from a sample

GSM = weight of the sample in grams ÷ its area in square metres.

• Measured in cm: GSM = weight × 10,000 ÷ (length × width).
• Measured in inches: GSM = weight ÷ (length × width × 0.00064516), since one square inch is 0.00064516 m².
• GSM cutter: the standard round cutter cuts 100 cm², which is 0.01 m², so GSM = weight × 100.

Weigh on a scale that reads to 0.01 g. On a 100 cm² disc every 0.01 g is 1 GSM, so a scale that reads only whole grams can be out by 50 GSM or more. Labs condition samples in the standard atmosphere of ISO 139 before weighing, as ISO 3801 requires for woven fabric, because moisture changes the weight.

Formula 2: GSM from EPI, PPI and yarn count

For woven fabric you can estimate GSM by adding up the yarn in one square metre. Each set of threads adds:

g/m² = threads per inch × 39.37 × (1 + crimp) × tex ÷ 1,000

39.37 turns threads per inch into threads per metre, (1 + crimp) adds the length each thread takes up as it bends (6% crimp is 1.06), and tex ÷ 1,000 is the weight of one metre of yarn. Do it for the warp (EPI) and the weft (PPI) and add the two. With the count in other units, the formula reads:

Worked example

The calculator opens with a polyester fabric: warp 75 denier at 110 EPI with 6% crimp, and weft 100 denier at 90 PPI with 5% crimp.

• Warp: 110 × 39.37 × 1.06 × 8.333 ÷ 1,000 = 38.25 g/m²
• Weft: 90 × 39.37 × 1.05 × 11.11 ÷ 1,000 = 41.34 g/m²
• GSM = 79.6

For cotton, a 40s × 40s fabric at 120 EPI and 60 PPI with 6% crimp both ways comes to (120 ÷ 40 + 60 ÷ 40) × 23.25 × 1.06 = 110.9 GSM.

Why the real GSM differs

• Sizing adds weight to the warp of grey fabric, and desizing in processing takes it off again.
• Dyeing, printing, coating and finishes add or remove weight. Weight reduction on polyester removes some fibre.
• Fabric shrinks in processing, so ends and picks per inch rise, and GSM rises with them.

Common mistakes

• Weighing one sample from near the selvedge. Take 3 to 5 from across the width and average them.
• Using loom settings instead of counting the threads per inch in the cloth with a pick glass.
• Mixing up count systems: Ne is indirect, so 40s is finer than 20s, while a higher denier is a thicker yarn.

When it is worth software

If you check GSM for every quality and every taka, a register soon stops being enough. Weaving and powerloom software keeps quality-wise GSM, taka production and yarn stock in one place. For the yarn side, the yarn count converter turns denier into Ne or tex, and the fabric metre to kg calculator turns GSM into weight per metre.

Sources: ISO 3801 (mass per unit area of woven fabric) and ISO 139 (standard atmospheres for testing textiles); GSM cutter area from cutter makers' specifications (100 cm², a 112.8 to 113 mm disc). The woven estimate matches the textbook form (EPI ÷ warp count + PPI ÷ weft count) × (100 + crimp %) × 0.2327. Checked 9 November 2026.