Little's Law was put forward and proved by John Little, a professor of Si Long School of Management at MIT, at 196 1. Its English name is Little's Law. This is a simple mathematical formula about the relationship between lead time and work in process, which points out the direction for the improvement of lean production. How to effectively shorten the production cycle? Little's law has clearly pointed out the direction. One direction is to increase production capacity, thus reducing the pace of production. The other direction is to reduce the inventory quantity. However, improvement often means increasing a lot of investment. In addition, although the increase of production capacity can shorten the production cycle, there is always a limit to the increase of production capacity, and we cannot tolerate that the production capacity far exceeds the market demand. Generally speaking, the production capacity of each company will remain basically unchanged for a certain period of time. In the long run, each company will strive to match its production capacity with market demand. Therefore, the most effective way to shorten the production cycle is to reduce the number of products in process.

Little's law applies not only to the whole system, but also to any part of the system.