Safety Stock

Safety stock = z · σ · √L - how many spares to carry above expected demand to cover lead-time demand variability.

MaintenanceInventory

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This calculator requires JavaScript to compute its result. The formula, symbols, and regulatory sources are shown in the Formula section below.

Formula, assumptions, and limits

SS = z \cdot \sigma \cdot \sqrt{L}

Symbol	Meaning	Unit
$z$	Normal-quantile for service level
$σ$	Demand volatility	units / period
$L$	Lead time	periods

Source: IACS UR Z18 - Critical equipment and spares

Safety stock = z \u00b7 \u03c3 \u00b7 \u221aL - how many spares to carry above expected demand to cover lead-time demand variability.