How it works
For independent daily demand variation and a fixed lead time, standard deviation scales with the square root of lead time and a chosen z multiplier. This form solves for daily demand standard deviation; enter the known quantities in Safety stock, Critical z multiplier, Fixed lead time.
Inputs and units
| Input | Example value | What to enter |
|---|---|---|
| Safety stock | 40 | Formula symbol: s. Enter a numeric value. Must be greater than zero. |
| Critical z multiplier | 2 | Formula symbol: z. Enter a numeric value. Must be greater than zero. Allowed range: 0.001–10. |
| Fixed lead time | 4 d | Formula symbol: l. Required unit: d. Must be greater than zero. Allowed range: 0.001–3,650. |
Worked example
Show example inputs and results
This example is generated by the same calculation engine using the starting values in the form. Your own inputs produce your own result.
- Safety stock
- 40
- Critical z multiplier
- 2
- Fixed lead time
- 4 d
Complete example results
- Daily demand standard deviation
- 10
Reading the result
The result solves for daily demand standard deviation from the entered quantities. Check the result unit and the formula conditions before using it.
Questions and answers
Can I use the example values for my own calculation?
The example values illustrate the calculation. Replace every input with your own information, especially dates, rates and the selected operation.
When can I use the daily demand standard deviation result?
You choose z; the tool does not verify service probability or the normal approximation. Variable lead times are excluded.
Why are some results rounded?
Results display up to 8 decimal places. Calculations use the unrounded values; very small values use scientific notation. JavaScript floating-point arithmetic can introduce tiny rounding differences.
Are my inputs sent to a server?
The calculator processes inputs in your browser. Its code does not send your values to a server.
Method sources: live.ocw.mit.edu