Ounces per square yard (oz/yd²)

Ounces per square yard (oz/yd²) is the customary-unit counterpart to GSM: weigh a one-yard-by-one-yard swatch of fabric on a scale calibrated in ounces and that’s the number. US apparel catalogs have used it for decades, so it’s the figure most American blank suppliers lead with — Gildan’s G500 is “5.3 oz,” Next Level’s 3600 is “4.3 oz,” Comfort Colors’ 1717 is “6.1 oz” — even when the same sheet also lists GSM in smaller print underneath.

The number tells you more than raw weight; a heavier oz/yd² fabric generally means denser yarn packing, which means less light passing through the shirt and less ink needed to hit full opacity, whether that’s a dark print on a light garment or the reverse. Two shirts at the same oz/yd² can still feel different depending on whether the yarn is ringspun or open-end, combed or carded — weight is the biggest lever, not the only one.

When a spec sheet gives a range like “5.0–5.3 oz,” that’s normal lot-to-lot variation in raw cotton, not a printing error — expect a few percent swing between dye lots of the same style. Use oz/yd² to shortlist blanks in the weight class you want, then check fiber content and knit type to finish the decision.

The mistake is treating a jump from 4.5 oz to 5.5 oz as minor — a full ounce per square yard is roughly a 20% weight increase, enough to change how a shirt drapes, prints, and holds up over years of washing.