What it is
Grams per square meter (gsm, g/m²) is fabric areal density. Ounces per square yard (oz/yd²) is the usual US denim label. 1 oz/yd² = 28.349523125 g / 0.83612736 m² ≈ 33.9057 g/m² from NIST ounce and yard. Not leather thickness, not cobbler units.
How to use
gsm / 33.9057 ≈ oz/yd². Example: 180 gsm ≈ 5.3 oz. The converter above uses the NIST-derived factor.
oz/yd² = g/m² × 0.02949352468
Example: 1 g/m² = 0.02949352468 oz/yd²
Common uses
T-shirt jersey is often 160-180 gsm; denim 300-500 gsm; lining 50-80 gsm. US denim is commonly labeled 10-14 oz. Use this when buying fabric and reading imported bolts.
Conversion tips
About 1 oz/yd² ≈ 33.9 gsm. 14 oz denim ≈ 475 gsm. Do not mix this column with denier or button ligne.