What size ratio should I use for a first underwear order?

Short answer: An even split across sizes is rarely right, because demand is usually concentrated in the middle of the range and falls away at the edges. Without sales history, a first ratio is an informed estimate that should be reviewed quickly after launch. Start with the market: the brand's target customers, their country and age, and the size chart you publish. ISO 8559-2 designates clothing sizes by body dimensions, and using body measurement ranges, such as waist and hip for lower-body garments, on the size chart helps customers choose correctly and reduces exchanges that distort early data. Next, use any information you have: sales of similar products in your existing range, retailer advice, marketplace size feedback, or the factory's experience of common size curves for that market, treating each as a guide rather than fact. Then weight the order towards the middle sizes, keep enough depth in edge sizes to test demand, and plan a quick reorder for the sizes that sell first. Remember that each size in each colour is a separate stock unit, and GS1 guidance is that each size and colour variant needs its own GTIN, so a wide range across many colours multiplies the stock units to manage.

Inputs for a first ratio

• Target customers and market.
• Published size chart in body measurements.
• Sales of similar products.
• Retailer, marketplace or factory guidance.

Shaping the ratio

• Weight towards middle sizes.
• Keep test quantities in edge sizes.
• Use the same ratio across core colours at first.

After launch

• Track sell-through by size weekly.
• Reorder the fastest sizes first.
• Adjust the ratio on the next order.

A worked example

As an illustration, a brand could place most of its order in M and L, smaller quantities in S and XL, and a test quantity in XXL, then compare sell-through by size after the first weeks before setting the reorder ratio.

Channel differences

Different channels can have different size curves. A retailer in one region may sell more small sizes than an online store with a wider audience, so plan ratios by channel when quantities allow.

Planning the first reorder

Because the first ratio is an estimate, plan the reorder at the same time as the first order. Ask whether fabric can be reserved for a quick top-up, and decide in advance which sales signal, such as a size reaching a set sell-through, will trigger the reorder.

Limits

No ratio is correct for every brand. Returns and exchanges can also shift demand between sizes, so review sell-through after returns, not only at first sale.

Facts, recommendations and uncertainty

Established: demand usually concentrates in middle sizes, and a size chart in body measurements helps customers choose. Recommendation: weight the first order to the middle and plan a fast reorder. Uncertain: the real size curve until sales and returns data arrive.

Sources and further reading

• ISO 8559-2:2025 — Size designation of clothes: primary and secondary dimension indicators
• GS1 — How many GTINs for a product with many sizes and colours

Standards and regulations are referenced by their published scope. Test parameters, cycles and pass levels should be agreed with your laboratory for the specific product; legal requirements should be confirmed for each destination market.