THE NUMBERS, EXPLAINED
How to use this calculator.
Steady flow inventory identity; gives mean demand, not a probability of availability during peaks.
Start with your inputs
Enter customer arrival rate (customers/hour), customers using a trolley (%), average trolley trip duration (minutes), return/reposition lag (minutes), available trolley fleet. Keep amounts in the units shown on each field. The example is a starting point, not a recommended value.
| Input | Example value |
|---|---|
| Customer arrival rate (customers/hour) | 120 |
| Customers using a trolley (%) | 50 |
| Average trolley trip duration (minutes) | 40 |
| Return/reposition lag (minutes) | 10 |
| Available trolley fleet | 45 |
A worked example
With the example inputs above, average trolley demand is 50. Change the inputs to explore your own scenario.
| Result | Example answer |
|---|---|
| Average trolley demand | 50 |
| Whole trolley provision for mean demand | 50 |
| Mean-demand fleet gap | 5 |
How this is calculated
Average trolley demand
Multiply trolley arrivals per hour by complete circulation time.
Whole trolley provision for mean demand
Round average concurrent demand upward.
Mean-demand fleet gap
Compare rounded demand with fleet availability.
Symbols and units
- a
- Customer arrival rate (customers/hour)
- b
- Customers using a trolley (%)
- c
- Average trolley trip duration (minutes)
- d
- Return/reposition lag (minutes)
- e
- Available trolley fleet
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 flow inventory identity; gives mean demand, not a probability of availability during peaks.
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?
Average trolley demand; Whole trolley provision for mean demand; Mean-demand fleet gap. 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 flow inventory identity; gives mean demand, not a probability of availability during peaks.
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.
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