THE NUMBERS, EXPLAINED
How to use this calculator.
Steady-state arrivals with one collection per item; mean inventory excludes peak buffers, oversize packages and abandoned mail.
Start with your inputs
Enter mail items received per day, handling minutes per incoming item, average storage duration (days), average occupied shelf volume per item (l), collection handling minutes per item. Keep amounts in the units shown on each field. The example is a starting point, not a recommended value.
| Input | Example value |
|---|---|
| Mail items received per day | 100 |
| Handling minutes per incoming item | 1.5 |
| Average storage duration (days) | 3 |
| Average occupied shelf volume per item (L) | 0.5 |
| Collection handling minutes per item | 0.5 |
A worked example
With the example inputs above, daily handling hours is 3.333333. Change the inputs to explore your own scenario.
| Result | Example answer |
|---|---|
| Daily handling hours | 3.333333 |
| Mean items held in storage | 300 |
| Mean shelf volume (L) | 150 |
How this is calculated
Daily handling hours
Include incoming processing and eventual collection handling.
Mean items held in storage
Multiply daily arrivals by mean storage duration.
Mean shelf volume (L)
Multiply circulating mail inventory by item shelf volume.
Symbols and units
- a
- Mail items received per day
- b
- Handling minutes per incoming item
- c
- Average storage duration (days)
- d
- Average occupied shelf volume per item (L)
- e
- Collection handling minutes per item
Use the units shown. A list keeps the order in which you enter its values. The symbol ^ means “raised to the power of”.
Assumptions and limits
Steady-state arrivals with one collection per item; mean inventory excludes peak buffers, oversize packages and abandoned mail.
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?
Daily handling hours; Mean items held in storage; Mean shelf volume (L). 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: Steady-state arrivals with one collection per item; mean inventory excludes peak buffers, oversize packages and abandoned mail.
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.
Further reading
MIT Operations Management: Queueing and Little’s Law ↗
Background reading; this does not imply endorsement or independent review of SumFizz.
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 →