What is Size curve?

If you sell apparel or shoes, sizes do not sell evenly. A t-shirt style might sell mostly mediums and larges, with fewer small and extra-large units. A size curve captures that pattern so you buy in the right proportions instead of guessing or ordering equal amounts of each size.

Use your past sales data to build the curve for each product or product group, then apply it when placing new orders. If your supplier sells in case packs with fixed size ratios, check whether that ratio matches your actual size curve. If it does not, you will end up overstocked in sizes that do not sell and out of stock in the ones that do.

Formula

Example

A store sells a hoodie in sizes S, M, L, XL. Over the last 100 units sold, 15 were S, 35 were M, 35 were L, and 15 were XL. The size curve is 15% S, 35% M, 35% L, 15% XL. If the owner orders 200 units for the next batch, they would buy 30 S, 70 M, 70 L, and 30 XL to match the curve.

Common mistakes

• Ordering equal quantities per size instead of following actual sales proportions.
• Using a supplier's standard case pack ratio without checking it against your own sales data.
• Not updating the size curve as a style ages or as customer demand shifts.

Size curve and SteadyShelf

SteadyShelf forecasts per variant, so it can apply a size curve automatically when suggesting order quantities for each size SKU.

SteadyShelf is launching on the Shopify App Store. Join early access to get the install link first.

Related terms

Size run · Variant · Demand forecasting · Case pack · Assortment planning

Full inventory glossary

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