Little's Law

LotT-en.01.md

LITTLE's LAW

The average number of work items in a stable system is equal to their average completion rate, multiplied by their average time in the system.

Problem Statement A:

At home, I have 12 bottles of whisky at my bar. I consume and purchase an average of 6 whisky bottles per year. What is the average time each whisky bottle stays in my bar?

Problem Statement B

At home, I have 12 bottles of whisky at my bar. In average, I finish (and purchase) one whisky bottle every two months. What is the average time each whisky bottle stays in my bar?

Variables

• Working in Progress: 12 botellas, (Problema A, B)
• Throughput: 6 botellas por 12 meses (Problema A)
• Average Cycle Time: 2 meses por botella (Problema B)

Solution 1

WIP = Throughput x Average Lead Time
12 bottles = 6 bottles /12 months x Average Lead Time,
Therefore, Average Lead Time = 24 months

Solution 2

Average Lead Time = WIP x Average Cycle Time
Average Lead Time = 12 bottles x 2 months/bottle
Therefore, Average Lead Time = 24 months

...

[WIP = Throughtput x Lead time] <=> [Lead Time = WIP x Cycle Time]

• Lead time is the time between the initiation and delivery of a work item.
• Cycle time is the time between two successive deliveries
• Throughput is the rate at which items are passing through the system.
• WIP - Work in progress; the number of work items in the system. Work that has been started, but not yet completed

¿What the Little's Law implies in the daily work?

The power of Little's Law Kanban teams is not its ability to predict WIP, Thoughput or Leadtime. The true power lies in its ability to influence team behavior with its underlying assumptions. In other words, if you want to:

• Increase Throughput then limit WIP.

• Speed up the process, i.e. reduce Lead Time, then once again limit the WIP.

• https://en.wikipedia.org/wiki/Little%27s_law

• http://www.caroli.org/little-law-cycle-time-and-throughput/