Deciding quantity per size is a forecast, and the default of splitting evenly across the range is almost always the least accurate option available.
Why even splits fail
Demand across a size range is not uniform. Middle sizes typically sell fastest, and the ends sell more slowly. An even split reliably produces stockouts in the middle and leftovers at the extremes.
What to base a ratio on
- Your own sales history, if you have any
- The demographics of your existing audience
- Category norms, used as a starting point rather than an answer
- The fit of the specific garment, since some styles skew
Fit skews the curve
An oversized garment sells differently across sizes than a fitted one, because customers select by intended fit rather than measurement. The same ratio will not suit both.
Plan for the reorder
If lead times allow reordering within a season, you can produce a tighter first run and replenish what sells. That is a substantially better use of capital than guessing deeply on the first attempt.
Record what actually happened
Sell through by size is the most valuable data a first run generates. Capture it deliberately, because it makes every subsequent forecast better.