Size safety stock and reorder point from demand, lead time, demand variability, and a z service factor.
| Safety stock | – |
| Reorder point | – |
Use this safety-stock calculator when demand per period and lead time are in matching units (for example daily demand and lead time in days). σ is the standard deviation of demand per period, not over the whole lead time. This is the common z × σ × √L sketch; it ignores supplier uncertainty as a separate term.
Safety stock = z × σ × √lead. Reorder point = demand × lead + safety stock. Typical z values: 1.28 ≈ 90% cycle service, 1.65 ≈ 95%, 2.33 ≈ 99%.
Demand / period: Average units used per period (day, week—same as lead).
Lead time: Periods until a replenishment arrives.
σ (demand): Standard deviation of demand in one period, in units.
z: Service-level factor from the normal table (unitless).
Safety stock: Extra units held against variability.
Reorder point: Inventory level that triggers a new order.
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