Efficiency · 02 / 07
Little’s law
In a stable system, the time an item takes to get through is the work in progress divided by the throughput. If capacity does not change, starting more things does not get more done: it only makes each one take longer.
L = λ · W · cycle time = work in progress / throughput
Try it
Raise the number of tasks in progress and see what happens to what comes out and to how long each one takes.
- In progress
- 4
- Throughput
- –
- Cycle time
- –
- Little’s law
- –
Where it applies
- A team with fifteen stories open at once takes three times as long to finish each one as with five.
- A legal department that takes on every contract at once stretches its response time without signing any more.
- Shipping each change on its own, instead of in a monthly bundle, cuts work in progress and lead time.
Where it comes from
Philip M. Morse posed it as a conjecture and John D. C. Little proved it in “A Proof for the Queuing Formula: L = λW” (Operations Research, 1961). Hopp and Spearman turned it into a management tool in “Factory Physics” (1996).
Bring it to your organization
In my workshops and diagnoses we work on this and other principles over your team’s real flow of work, with your data rather than the simulation’s. See services or write to me.