Little’s Law, explained.
Little's Law connects average work in a stable system, average throughput, and average time in the system: L = λW.
Why it happens
If items enter and leave at a stable long-run rate, spending longer in the system means more items are present on average. The relationship concerns averages over a consistent boundary, including waiting if waiting is inside that boundary.
In a stable queue, average inventory equals throughput multiplied by average time in the system.
Read the result
Compare the number of items in the system, the throughput rate, and the implied time. Keep units consistent and avoid treating a steadily growing backlog as a stable queue.
A worked example
A team's open work
A team completes eight tasks per week and has 24 tasks in progress on average.
Little's Law gives an average time in the system of 24 ÷ 8 = three weeks.
Reducing open work can reduce lead time if throughput and the system boundary stay comparable.
OPTIONAL DEEPER DETAILGo deeper: inside the model
Inside this model
W=L/λ, where L is average items in the system and λ is completed items per hour. The chart shows time for a range of average inventories at the chosen throughput.
Where this idea is useful
A practical use
Use tickets in progress and tickets completed per day to estimate average response time.
A common misconception
“Every task will finish in exactly three weeks.”
The relationship describes averages. Individual tasks can vary widely, and changing the process can change throughput too.
What this explanation leaves out
- The identity uses long-run averages in a stable system; a growing backlog cannot be summarized by one steady-state W.
Does the arrival rate always equal throughput?
In a stable system over a suitable observation period, they balance on average. If arrivals persistently exceed departures, the backlog grows and a stationary interpretation is inappropriate.
Have you measured waiting and active work within the same boundary?
Associated thinkers
Further reading
Explore the original research or the teaching reference behind this experiment.