Glossary
Size curve
How a style's sales split across its sizes, as a share of units. The curve you sold is the best guide to the curve you buy next.
Formula
Share of a size = units sold in that size ÷ units sold in every size × 100
Worked example
A dress sells 400 units: XS 32, S 88, M 120, L 104 and XL 56. Its curve is 8%, 22%, 30%, 26% and 14%. Bought flat at 20% a size, its M and L sell out first.
In fashion, footwear and sportswear
Footwear curves run wider and steeper than apparel, and a best seller's middle sizes can carry a third of its units. Build the curve from weeks when every size was in stock.
Where it misleads
A size that sold out early looks unpopular. Count only the weeks a size was available, and normalise size names (M, Medium, UK 10) before you add them up.