THE NUMBERS, EXPLAINED
How to use this calculator.
Assumes independent daily demand and fixed lead time. The z-score is supplied by you; this is not a universal service guarantee.
Start with your inputs
Enter daily demand standard deviation, lead time (days), service z-score. Keep amounts in the units shown on each field. The example is a starting point, not a recommended value.
| Input | Example value |
|---|---|
| Daily demand standard deviation | 10 |
| Lead time (days) | 4 |
| Service z-score | 1.65 |
A worked example
With the example inputs above, safety stock (units) is 33. Change the inputs to explore your own scenario.
Putting the example numbers into the formula
Safety stock (units)
(1.65) × (10) × sqrt((4)) = 33
| Result | Example answer |
|---|---|
| Safety stock (units) | 33 |
How this is calculated
Safety stock (units)
c × a × sqrt(b)
Symbols and units
- a
- Daily demand standard deviation
- b
- Lead time (days)
- c
- Service z-score
Use the units shown. A list keeps the order in which you enter its values. The symbol ^ means “raised to the power of”.
Calculation steps and notation
sqrt(x) is the non-negative square root of x.
Assumptions and limits
Assumes independent daily demand and fixed lead time. The z-score is supplied by you; this is not a universal service guarantee.
Calculations use the values you enter. Blank or invalid inputs show an error instead of silently substituting zero. Results are displayed to useful precision; calculations retain the underlying numeric precision.
Questions about this tool
What does the result tell me?
Safety stock (units). The result applies to the method and inputs described above. Check the units and assumptions before using it in a decision.
Why might another calculator differ?
Differences in units, rounding, timing or model definitions can produce different answers. Compare the input definitions and the method, rather than only the final number. For this tool: Assumes independent daily demand and fixed lead time. The z-score is supplied by you; this is not a universal service guarantee.
Are my inputs stored or sent to AI?
Calculations on this page happen in your browser. The separate AI question finder sends its submitted conversation to OpenAI; these calculator fields are not sent. Favourites and recent tool names are stored locally. A shared link contains the inputs you choose to include.
Review status
Software example and browser checks are recorded in our quality report. No external expert review is claimed. Created with coding assistance; calculations run as ordinary browser code.
Read the quality report →