This is a question I grappled with as well. Initially it was easy because when you order from a pre-existing clothing line to carry their products as part of your online store, for example, they provide “size packs” in a pre-existing formula. Meaning, you have to buy a minimum of 6-8 garments, split into sizes. The size packs are often split like this:
XS (1) S (2) M (2) L (2) XL (1) A standard junior or “missy” pack is S (2) M (2) L (2)
We have found that a size pack closer to this is more effective:
XS (1) S (2) M (3) L (1) XL (1) sometimes, we didn’t order an XL depending on the style.
Once you have established your target audience (are they women in their teens? Twenties? Thirties?) you will know what is the most popular size. For us, with a young woman demographic, S definitely sold out the most quickly, followed by M. The odd sizes sat on the shelves for quite a bit longer.
We rarely ordered more than 3 size packs to start out. You don’t want inventory and large amounts of money just sitting on your shelves. It’s better to sell-out that to be over-stocked.