Work in Process Calculator
Little’s Law relates the average number of items in a stable system to throughput rate and average time in the system.
How to use this calculator
- Enter average throughput in units per day and average flow time in days.
- Check that every input uses the stated units and covers the same period, population or project scope.
- Change one assumption at a time when comparing scenarios.
Formula used by work in process calculator
Average WIP = throughput rate × average flow time
- Average WIP = throughput rate × average flow time
- The relationship assumes a stable system over the measurement period. Changing demand, rework, batching and mismatched definitions affect usefulness.
- Inputs are validated against the tool-specific constraints; displayed results are rounded for readability.
Worked examples
Worked example
A process averaging 180 units per day with 2.5 days of flow time has estimated average WIP of 450 units.
The calculator multiplies a throughput rate by flow time after you enter consistent time units.
The calculator multiplies a throughput rate by flow time after you enter consistent time units.
Understanding the result
Little’s Law relates the average number of items in a stable system to throughput rate and average time in the system.
The relationship assumes a stable system over the measurement period. Changing demand, rework, batching and mismatched definitions affect usefulness.
Important notes
The relationship assumes a stable system over the measurement period. Changing demand, rework, batching and mismatched definitions affect usefulness.
Treat the result as an estimate for the assumptions entered; verify important specifications against the relevant source or professional guidance.
Frequently asked questions
Does WIP mean inventory only?
It usually includes all work currently inside the defined process, not only finished stock.
Can I use mismatched periods?
No. Throughput and flow time must use matching units and a consistent process boundary.
How should I use this result?
Enter average throughput in units per day and average flow time in days.
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Related explanations
Learn the method behind the number or compare the terminology before using the calculator.
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This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.