Little’s Law

What is Little’s Law?

During the mid of the 1900s, John little presented a law which is clearly related to business community. In this law, he presented that the company have equal ratio between the multiplication of rate of the customer arrivals by the time which a customer spends and regular number of customers of company, it is called Little’s law.

Its commonly used expression is L = λW, which is explained like this,

• “L” shows the average number of customers,
• “λ” is denoted for the customers arrival average and
• “W” is for time which customer spends in the system.

When the number of customers are increasing in a system and the arrival rate remains constant then average time of the customer will be increasing in the system. Simply we can say that when the number of customers is increased it means that the time required to serve each of them is also increased.

How is it used in Kanban?

If little’s law is used in Kanban it make sense and relationship between, average number of customers, average rate of customers and time spent by the customers in the system.

If customers arrive at the rate of 10 per hour, staying average is 0.5 per hour. Find the average number of customers in the system.
Here, λ= 10, W= o.5 then L=?

L= λ*W
L=10*0.5
L=5

There are different terms use in Kanban according to the Little’s law. The most common term WIP, Work in Progress is used.

WIP= rate of customers * spending time by customers, here WIP=L

The number of items on which team is working is denoted as WIP. In Kanban different things can be taken as a measurement unit such as, situations, cards, stories related users and more.

Why it matters?

Any system that mean waiting time then Little’s Law can be used there, in the real world situations measurement of inflow is difficult than measurement of outflow.  This is a general formula and its generality makes it easy to use and to be in different time related situations.

— Slimane Zouggari