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
oz/yd² × 33.9057 ≈ gsm. Example: 12 oz ≈ 407 gsm (mid-weight denim). The converter above uses the NIST-derived factor.
g/m² = oz/yd² × 33.90574747
Example: 1 oz/yd² = 33.90574747 g/m²
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.