Little’s Law Calculator
Compute WIP, throughput, or flow time using Little’s Law for any stable process or queue.
How it works
- 1Select which variable you want to solve for — WIP, throughput, or flow time.
- 2Enter the two known values into the input fields.
- 3The result updates instantly using Little’s Law: WIP = Throughput × Flow Time.
Use cases
- Estimate queue depth in a call centre given arrival rate and average handle time.
- Find the throughput a production line must achieve to hit a target WIP level.
- Calculate how long a unit spends in a process given WIP count and throughput rate.
Frequently asked questions
What is Little’s Law?
Little’s Law states that in any stable system, WIP = Throughput × Flow Time. For example, if a factory produces 10 units per hour and each unit spends 5 hours in the system, then 50 units are in process at any moment.
Does Little’s Law require a specific distribution of arrivals or service times?
No. It holds for any stable system regardless of the arrival or service-time distribution — Poisson, deterministic, or otherwise — as long as the long-run average rates are constant.
How can I use this to reduce lead time?
Rearranged: Flow Time = WIP ÷ Throughput. If throughput is fixed, cutting WIP directly cuts lead time. This is the basis of lean manufacturing: limit WIP to speed up flow.
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