Safety Stock Calculator
Calculate the safety stock and reorder point for any SKU in seconds. Choose between a quick estimate or a statistically rigorous calculation.
Inputs
Use when you know demand variability but not lead time variability.
Tip: if you don't know σ, use ~30% of average demand as a starting estimate.
Formula used (simple mode)
SS = Z × σd × √LT
ROP = (D × LT) + SS
Where Z = service level factor, σd = demand std dev, LT = lead time in days, D = avg daily demand
Inputs
Accounts for variability in both demand and lead time — statistically more accurate.
Formula used (advanced mode)
SS = Z × √(LT × σd² + D² × σLT²)
ROP = (D × LT) + SS
Accounts for variability in both demand and lead time simultaneously
Safety Stock
—
units
Reorder Point
—
units
Z Factor
—
service level
Inventory Level Visualization
Sawtooth inventory model — order is triggered when stock hits the Reorder Point
Calculation breakdown
Safety Stock at Different Service Levels
| Service Level | Z Factor | Safety Stock | Reorder Point |
|---|
What these numbers mean
Safety stock is the buffer inventory that protects against stockouts during demand spikes or supplier delays. The reorder point tells you when to place a new order — once stock drops to this level, you have exactly enough stock to cover demand during the replenishment lead time plus your safety buffer.
Need help implementing safety stock in your WMS or ERP?
Most WMS platforms automate safety stock calculations and trigger replenishment orders automatically. See our guides on best WMS software and safety stock formulas explained.