01
Formula used
Safety stock = z-score × daily demand standard deviation × √ lead time in days.
If lead time also varies materially, use a model that includes both demand and lead-time variance.
Inventory planning tool
Safety stock calculator
Estimate the inventory buffer needed to absorb demand variability during supplier lead time.
This calculator uses a common statistical model: service-level z-score multiplied by daily demand standard deviation and the square root of lead time. It assumes independent daily demand and stable lead time.
Demand and policy
Estimated result
Safety stock112 units
Rounded to a whole unit.
Service factorz = 1.65
Lead-time square root3.7
02
Use it when
- Setting an initial buffer for a SKU with usable demand history
- Comparing the inventory effect of different service levels
- Reviewing whether an existing buffer matches observed variability
03
How to interpret the result
- Higher service levels require a larger buffer.
- Longer lead times amplify demand uncertainty.
- The result should be rounded to the practical purchase or stocking unit.
Soberan
From calculation to operational decision
Use the result as a starting point, then keep data, policy, exceptions, and approvals inside the actual workflow.
Explore inventory optimization →Frequently asked questions
What service level should I use?
Choose a target based on stockout cost, customer promise, margin, and replenishment flexibility. A higher target is not automatically better.
How do I calculate daily demand standard deviation?
Use a consistent series of daily demand observations and calculate their sample standard deviation. Remove data errors, but do not remove real variability.
Does safety stock equal the reorder point?
No. Safety stock is the buffer. The reorder point adds expected demand during lead time to that buffer.