Little’s Law Flow Time Calculator
Use Little’s Law to estimate average time in a stable system from the average number of items in the system and throughput rate.
How to use this calculator
- Enter average work in process (items), average throughput (items per hour); check the units and use values from the same period or scenario.
- Review the result and intermediate values; change one input at a time when comparing scenarios.
- Keep the stated formula and assumptions with any result you share.
Formula and method
Average flow time = average work in process ÷ average throughput rate, provided both metrics cover the same stable process and unit definitions.
- Estimated average flow time is 3 hours.
- Little’s Law describes long-run averages under consistent system boundaries. It does not predict individual completion times or diagnose variability.
Worked examples
Worked example
An average of 42 items is in process while 14 items complete each hour.
Estimated average flow time is 3 hours.
Estimated average flow time is 3 hours.
Understanding the result
Estimated average flow time is 3 hours.
Little’s Law describes long-run averages under consistent system boundaries. It does not predict individual completion times or diagnose variability.
Important notes
Little’s Law describes long-run averages under consistent system boundaries. It does not predict individual completion times or diagnose variability.
Use measured inputs and verify that the model matches the situation before making an operational, financial or technical decision.
Frequently asked questions
Does this equal processing time?
Not generally. Flow time can include waiting, queues, processing and other time within the defined system.
Can throughput be zero?
No; a positive throughput is required for a finite estimate.
What should I check before relying on this result?
Verify units, input definitions and assumptions against your real data or the relevant product, service or professional guidance.
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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.