Size Curve Allocation Formula
How apparel buyers and allocators translate a size curve into per-size buy units — and why channel-specific curves outperform industry averages.
What Size Curve Allocation measures
Size curve allocation is the unit distribution across sizes for a given buy. It is applied at the style-color level and drives both the buy PO breakdown and the door-level ship plan.
Units per Size = Total Buy × Size % from CurveThe size curve itself — what percentage each size takes — must come from historical sell-through data by channel. Wholesale curves differ from DTC, and often differ by account within wholesale.
Worked apparel example
A style with a 1,000-unit buy and a size-M percentage of 22%.
M Units = 1,000 × 0.22 = 220 units
Apply the full curve — XS 8%, S 20%, M 22%, L 22%, XL 18%, XXL 10% — and the total sums to 1,000. If the curve does not sum to 100%, the buy rolls up wrong and the PO is short.
Allocate 220 units to this size. Use the actual customer-purchase size curve by channel, not the industry-average curve.
Failure modes we see
Industry-average size curves applied to every channel. A brand uses the same curve for DTC, mall stores, and a premium wholesale account. DTC runs bigger sizes; premium wholesale runs smaller. The blended curve misses both — over-stocking smalls online and missing mediums in-store.
How RetailNorthstar handles size curves
The system maintains size-curve libraries by channel, by account, and by size classification. Curves are recalculated from trailing sell-through. At every buy or reallocation, the right curve is applied automatically.
Related formulas
- Buy Quantity — the total units to distribute
- Style-Color Depth — how deep the curve gets applied
- Fair-Share Allocation — the next step: spreading units across doors
See size curves live by channel and account — trained on your sell-through, not industry averages.
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