Little's law: A very short introduction

In a firm managers have greater responsibility, he/she have to control everything coming under her/his responsibility. In a system there are certain number of people who works in that system along with it there would be a flow people in and out of the system. And some may spend in the system until their work get done. Manager should keep these things under control.
Business managers usually uses a formula to control the flow of customers into and out of their system which was first proposed by American operations research professor John Dutton Little. After his name this formula is known as Little’s formula. This formula has a specific rule which states that the average number of people in a system is equal to the average rate at which people enter into the system multiplied by the average time that an individual spends within it .
L=λW
where, L=average number of peoples in the system , λ= rate at which average customers arriving, W= average waiting time for a customer
In operations management field this formula is quite popular and known as Little’s law. This law helps managers to estimate average waiting time a customer will likely experience before receiving a service.

The only requirements are that the system be stable and non-preemptive

References: wkipedia, MIT