Safety Stock
Safety stock = z · σ · √L - how many spares to carry above expected demand to cover lead-time demand variability.
Z-factor for service level
1.64 -
Safety stock
5.7units
Formula, assumptions, and limits
Assumes normal distribution of demand over lead time. Critical spares (main-engine piston rings, turbocharger rotors) may warrant z = 2.33 (99 %) or bespoke analysis. Long lead times dramatically inflate SS.
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| Normal-quantile for service level | - | lookup | |
| Demand volatility | units / period | history | |
| Lead time | periods | procurement |