Checklist
Measure arrival rate, work in progress, and cycle time together
Flow variables constrain one another.
When it fits
- When teams argue about speed using only one flow metric.
When to avoid it
- Queueing equations have specific assumptions. Use them for directional reasoning and measurement design, not as exact forecasts for arbitrary multi-stage knowledge work.
Checklist
- Fix one process boundary.
- Measure average completed rate.
- Measure average WIP.
- Measure average elapsed time and check consistency.
Why it matters
Track throughput or arrival rate, average work in process and average time in system on the same boundary. Use Little's Law as a consistency check when assumptions are approximately appropriate.
An example
A workstream reports ten items finished per week, twenty items active and roughly two weeks average elapsed time; the three measures tell a coherent story.
Check your result
The three quantities use the same boundary and time basis and gross inconsistencies are investigated.
Keep this limit in mind
- Queueing equations have specific assumptions. Use them for directional reasoning and measurement design, not as exact forecasts for arbitrary multi-stage knowledge work.
Connected ideas
Useful withTreat growing WIP as a delay signal
Evidence and sources
Supports
Little's Law relates long-run average work in a stable system to arrival/throughput rate and average time in system as L = λW under stated mathematical conditions.
The relation does not identify root cause, queue discipline or the correct intervention; workplace applications must respect the assumptions.
A Proof for the Queuing Formula: L = λW · Abstract