How do you calculate size curve inventory?

Multiply daily sell-through by replenishment lead time to get cycle stock, then add the safety stock buffer. The required inventory equals what sells during the lead time plus your protection against variability.

What is cycle stock versus safety stock?

Cycle stock covers expected sales while a replenishment order is in transit; safety stock is the extra buffer for demand spikes and late deliveries. The buffer is what keeps a size from going to zero on a bad week.

Why size inventory per size instead of per style?

Because sell-through is wildly uneven across a size curve. The middle sizes can turn three to four times faster than the smallest and largest, so a single style-level number guarantees broken curves.

How does lead time affect required inventory?

Cycle stock scales directly with lead time, so a longer replenishment lead time forces more pairs on hand. Cutting lead time is often the cheapest way to shrink inventory without raising stockout risk.

What is a good safety stock buffer for footwear?

It depends on demand variability and service target, but planners commonly set it to cover one to two weeks of a size's sell-through. Tighten it for stable basics and widen it for fashion styles with spiky demand.

How do I keep a size curve from breaking?

Set per-size reorder points using this calculation, monitor the fastest-moving sizes most closely, and replenish before any core size hits its safety buffer rather than waiting on a style-level trigger.

Leather, Footwear & Accessories Manufacturing calculator

Size Curve Inventory Calculator

Size curve inventory sizing tells a footwear planner how many pairs to hold so a style stays in stock across its full size run while replenishment is in transit. It combines cycle stock (what sells during the lead time) with a safety buffer that absorbs demand spikes and supplier variability. Allocation and demand planners use it to avoid the classic footwear failure mode: plenty of total units but broken size curves, where the popular middle sizes sell out and only the extremes remain. It matters because a broken size run kills sell-through even when aggregate inventory looks healthy.

What this calculator does

Calculate required inventory levels across your footwear size curve by combining daily sell-through rate, supplier replenishment lead time, and safety stock for demand variability. Ensures adequate coverage for each size without overstocking slow-moving sizes.
Use this when planning size-run inventory for a new season, setting reorder points by size, reviewing safety stock levels after a lead time change, or preparing inventory budgets for warehouse capacity planning.
It computes required inventory as cycle stock (daily sell-through times lead time) plus a safety stock buffer.

Formula used

Cycle stock = daily sell-through rate x replenishment lead time
Required inventory = cycle stock + safety stock buffer

Inputs explained

Daily sell-through rate:
Replenishment lead time:
Size-curve safety stock buffer:

How to use the result

Use it when setting replenishment targets or reorder points for a footwear size curve or a single key size.
It applies one sell-through rate and buffer; real size curves need this run per size because the middle sizes turn far faster than the extremes.

Common questions

How do you calculate size curve inventory? Multiply daily sell-through by replenishment lead time to get cycle stock, then add the safety stock buffer. The required inventory equals what sells during the lead time plus your protection against variability.
What is cycle stock versus safety stock? Cycle stock covers expected sales while a replenishment order is in transit; safety stock is the extra buffer for demand spikes and late deliveries. The buffer is what keeps a size from going to zero on a bad week.
Why size inventory per size instead of per style? Because sell-through is wildly uneven across a size curve. The middle sizes can turn three to four times faster than the smallest and largest, so a single style-level number guarantees broken curves.
How does lead time affect required inventory? Cycle stock scales directly with lead time, so a longer replenishment lead time forces more pairs on hand. Cutting lead time is often the cheapest way to shrink inventory without raising stockout risk.
What is a good safety stock buffer for footwear? It depends on demand variability and service target, but planners commonly set it to cover one to two weeks of a size's sell-through. Tighten it for stable basics and widen it for fashion styles with spiky demand.

Last reviewed 2026-05-12.