Calculate safety stock from sales variability, supplier lead time and your target service level (Z × σ × √lead time). Free, no sign-up.
OmniRestock’s safety stock guide recommends the service-level formula for most ecommerce SKUs. The older max−average shortcut usually overstocks.
Safety stock = Z × σdemand × √lead time
Max daily sales × max lead time − average daily sales × average lead time pads every SKU for the worst day and the worst supplier delay at once. That often ties up cash in slow movers. Use it only when you lack enough history to estimate σ.
Read the full walkthrough in the safety stock guide, or pair this buffer with the reorder point calculator.