Fabric GSM calculator
Fabric weight as mass per unit area from a weighed sample of known size, in g/m² and oz/yd².
How this is calculated
GSM = sample weight (g) ÷ sample area (m²). Areas are converted with 1 m² = 10,000 cm² and 1 in² = 6.4516 cm²; weights with 1 oz = 28.3495 g. Ounces per square yard = GSM ÷ 33.906, since 1 oz/yd² = 28.3495 g ÷ 0.836127 m².
Worked example. A 100 cm² (0.01 m²) disc weighs 1.85 g. GSM = 1.85 ÷ 0.01 = 185 g/m², which is 185 ÷ 33.906 = 5.46 oz/yd².
Questions
- Why is the round cutter 100 cm²?
- Because 100 cm² is one hundredth of a square metre, the sample weight in grams multiplied by 100 is the GSM. A 1.85 g disc is a 185 GSM fabric.
- Does moisture matter?
- Yes. Cotton can change weight by several percent with humidity. Test standards condition samples in a standard atmosphere (20 °C, 65% RH) before weighing; results from an unconditioned sample on a humid floor will read heavy.
- How many samples should I cut?
- Take several specimens across the width, avoiding the selvedge, and average them. One disc tells you about one spot of the roll.
Sources & verification
Mass per unit area is defined in ASTM D3776/D3776M (Mass Per Unit Area (Weight) of Fabric) and ISO 3801 for woven fabrics. Unit factors are the exact international definitions of the ounce, yard and inch. The worked example is recomputed in the automated tests.