How do I choose zipper size by garment weight?

Q: How do I choose zipper size by garment weight?

The reliable rule is to match chain size to fabric weight and to the load the opening will carry. For light fabrics under about 150 g/m2, such as chiffon, lining and shirting, a #3 keeps the seam flat and avoids a stiff ridge. For mid-weight fabrics of roughly 150 to 350 g/m2, including most trousers, casual jackets and skirts, #5 is the standard.

Above about 350 g/m2, or whenever the zipper sits on a high-stress opening, move up. Heavy denim, wool coats, workwear and puffer jackets generally use #8, and #10 appears on luggage, upholstery and very heavy outerwear. Metal chains can often run one size smaller than coil for the same strength, because their teeth are denser.

Two corrections override weight. First, a curved or concealed opening needs a finer, more flexible chain, so stay at #3 or #4.5 even on heavier cloth. Second, childrenswear and safety-critical openings should follow the applicable standard rather than an aesthetic preference. Always test the chosen size on a sewn sample under load before committing to bulk.