Size curves and prepacks: splitting a wholesale order without losing margin

A store orders ten units of a pair of trousers. The question is how many in XS and how many in L. That split decides what it will sell at full price and what it will mark down at the end of the season. For the brand, adding up all those answers sets the quantities sent to the factory. The size curve is therefore as much a sales matter as a production one, and it is settled at the exact moment the sales rep fills in the grid with the buyer.

What is a size curve?

The size range, or size run, is the list of sizes a style comes in: XS to XL, 34 to 46, or 36 to 41 for shoes. The size curve says how a quantity is split across those sizes, in units or as percentages.

It is often written as a ratio. The 1-2-4-3-2 curve means one piece in XS, two in S, four in M, three in L and two in XL. The size range appears on the linesheet, the document that presents the collection to buyers with its styles and prices. The curve, on the other hand, is decided when the order is placed, and that is often where the store’s margin is made or lost.

What are sizes based on? Standards and body measurements

A size is not a universal measurement. The European EN 13402 series designates sizes from body measurements rather than from garment dimensions. Its Part 3, in its 2017 version, provides tables of body measurements and intervals for men, women, children and infants. The international standard ISO 8559-2, revised in 2025, for its part specifies the primary and secondary measurements to indicate for each type of garment.

In practice, however, every brand keeps its own grading. One brand’s M is not the same as the M of the brand on the next stand, and its sales curve reflects that.

Body measurements themselves change over time. In France, the French Textile and Clothing Institute (IFTH) ran a national sizing survey: 11,562 people were measured with 3D body scanners at 37 locations between April 2003 and April 2005. Studies of this kind mainly help brands adjust their patterns. For the order curve, they are above all a reminder that a split inherited from ten years ago deserves to be checked.

Prepack or ordering by the unit: what should you offer buyers?

A prepack is a fixed bundle: a number of pieces split according to a set curve, sometimes across several colours, which the buyer orders in multiples. Ordering by the unit, by contrast, lets the buyer enter the quantity they want in each size and each colour.

Many brands offer both options. The sales rep puts forward a recommended prepack to move fast, and the buyer can still edit it or order by the unit above a certain volume.

Worked example: a 12-piece prepack from XS to XL

Take a 12-piece prepack on the 1-2-4-3-2 curve. A store orders three packs in two colours, i.e. six prepacks.

The store receives 72 pieces, 24 of them in M. The size of the pack also weighs on the buying decision. A 12-piece prepack at €40 wholesale (excl. VAT) already comes to €480, and the order of six prepacks reaches €2,880 excl. VAT. That amount may be enough to clear a minimum order, or on the contrary put the prepack out of reach of a small store that only wants one colour.

How to calculate a size curve from sales history

The method comes down to five steps, to be repeated for each product family.

1. Start from in-store sales when you have them, not just from orders. An order tells you what the buyer bought, a sale tells you what the end customer took home. Sell-through by size, meaning the share of stock that was sold, is the best data available.
2. Group by product family and by fit. Slim-fit trousers and an oversized sweater do not share the same curve.
3. Correct for stockouts. A size that sold out in three weeks was underestimated, and its sales do not measure real demand.
4. Convert to percentages, then round to a whole pack. Out of 240 pieces sold, including 18 in XS, 42 in S, 78 in M, 63 in L and 39 in XL, the shares are 7.5%, 17.5%, 32.5%, 26.25% and 16.25%. Scaled to 12 pieces, they give 0.9 / 2.1 / 3.9 / 3.15 / 1.95, rounded to 1-2-4-3-2: the total is 12 again.
5. Review the curve every season and compare it with results. A curve is calibrated over time, not set once and for all.

When rounding doesn’t add up

Rounding sometimes gives 11 or 13 pieces for a 12-piece pack. In that case, adjust the size whose decimal was closest to 0.5, favouring the core sizes: one extra piece in M sells more easily than one extra piece in XS. Also keep at least one piece in every size of the range, otherwise the store will never be able to test the extreme sizes.

Back to the ten-piece trousers order with the same shares. The calculation gives 0.75 / 1.75 / 3.25 / 2.625 / 1.625, which rounding turns into 1-2-3-3-2, i.e. 11 pieces. L and XL have the decimals closest to 0.5. To keep the extra piece in the core sizes, you remove the piece in XL: the pack becomes 1-2-3-3-1, i.e. 10 pieces, with at least one piece per size.

Adapting the size curve to each account

An average curve is a starting point. Four criteria justify correcting it account by account.

• The country. Average body shapes and sizing habits vary from one market to another. A curve built in France should be checked before it is used for export, just like the prices and currencies covered in our guide to selling wholesale internationally.
• The customer profile. A store with a younger or sportier clientele does not sell the same sizes as a classic town-centre boutique.
• The type of store. A department store often covers the whole size range, a concept store picks the core sizes, an online retailer needs depth in every size.
• The point in the season. The pre-collection order covers the size range, while replenishment focuses on the sizes that sell.

Footwear and jewellery: shoe sizes and ring sizes

The logic stays the same, with different grids. In footwear, the curve is spread across shoe sizes, often including half sizes, and the system changes from country to country. European sizing is based on the Paris point, two thirds of a centimetre. UK and US sizes also coexist, as does Mondopoint, defined by the ISO 9407 standard (2019 edition), which expresses the size as the length of the foot in millimetres: a 260 mm foot takes a 260.

Half sizes multiply the columns of the grid. A curve designed for one country therefore has to be converted, not copied, for another.

In jewellery, the ISO 8653 standard (2016 edition) defines ring size by its inner circumference in millimetres, over a range from 41 to 76. Other systems coexist from country to country. Many brands limit their rings to a few sizes, or offer adjustable styles to avoid unsold stock.

A curve that is too spread out runs into the factory’s minimums

The sum of the orders, size by size and colour by colour, becomes the production order. Yet the factory often imposes its own minimums, per colour or per style. A curve that is too spread out scatters the quantities: the extreme sizes do not reach the factory minimum, and the brand has to choose between overproducing, paying a surcharge or dropping a size.

Prepacks that are consistent from one account to the next have the opposite effect. They pool the quantities and make production more predictable. One more reason to settle the size range and the prepacks before the selling campaign, not during it, along with the other points to prepare before a trade show.

Five mistakes that skew the size split

1. Applying the same curve to every style, whatever its fit.
2. Building the curve on past orders without accounting for stockouts or markdowns.
3. Imposing an oversized prepack that forces a small store to take sizes it does not sell.
4. Showing a prepack without showing what is inside. At a trade show as in a digital showroom, the buyer must see how many pieces they get in each size.
5. Correcting quantities by hand in a spreadsheet after the order, at the risk of sending the factory figures that differ from those the customer signed.

Sales first, prepacks second

A brand that wants a more reliable size split therefore starts with its sales data, corrected for stockouts, then sets one curve per family and per fit. From there it derives prepacks that fit its own minimums and the factory’s, and keeps ordering by the unit for key styles and for accounts that know their customers. Finally, it tests each curve against the following season’s sales. The terms used here, from MOQ to sell-through, are explained in our wholesale glossary.