Enter your own numbers below to calculate a safety stock buffer for a single SKU. See the safety stock glossary page for how the formula works, or the reorder point calculator to turn this into a full reorder point.
Z-score for 95% service level
1.64
Recommended safety stock
34.8 units
How to use this number
Add this safety stock figure to your expected demand during lead time (average daily usage × average lead time) to get a full reorder point. Run this calculation per SKU, since demand variability and lead time both differ by product—a single safety-stock number applied across your whole catalog under-buffers volatile items and over-buffers stable ones.
Revisit the inputs periodically. A supplier whose lead time lengthens, or a product whose demand becomes more volatile, both mean the old safety stock number is no longer sized correctly.
Frequently Asked Questions
What formula does this safety stock calculator use?
Safety Stock = Z-score × Standard Deviation of Daily Demand × √(Average Lead Time in Days). The Z-score corresponds to your chosen service level (e.g., 1.65 for 95%), reflecting how much buffer is needed to cover demand variability during lead time.
What service level should I use?
Higher service levels (99%+) mean fewer stockouts but require more safety stock and tie up more cash. 90-95% is a common starting point for most small-business SKUs; reserve 98-99%+ for critical, high-margin, or hard-to-substitute items.
Where do I get my demand standard deviation?
Calculate it from recent daily (or weekly) sales history for the specific SKU—most spreadsheet tools have a STDEV function. A rough estimate works, but the more variable your actual demand, the more this number matters to get right.
Does this calculator save my numbers?
No. This is a client-side calculation only—nothing is sent to a server or saved. Refreshing the page resets it to the defaults.
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