Enter the average arrival rate into and out of the system and the average time an item spends in the system to calculate the average number of items work in the process.

## Little’s Law Formula

The following formula is used to calculate the average WIP of a system using Little’s law.

L (WIP) = λ * W

- Where L is the average number of items within a system
- λ is the arrival rate/output rate of items into the system
- W is the average time an item spends in a system

To calculate the average number of items within a system from Little’s law, multiply the arrival rate by the average time an item spends in a system.

This formula can then be simplified to the following:

WIP = T * LT

- Where WIP is the work in progress
- T is the throughput
- LT is the lead time

## Little’s Law Definition

Little’s law states that the total average number of items within a system or process is equal to the product of the arrival rate(and output rate) of items and the average time an item spends in a system.

## When to use Little’s Law?

Little’s law is used to calculate the average number of items that are work in progress at any given time within a supply chain. Use it to better understand where bottlenecks are occurring in your business.

## What does Little’s Law State?

Little’s law states that the total work in progress is equal to the product of the throughput and the lead time.

## Little’s Law Example

How to calculate lead time using Little’s law?

**First, determine the work in process.**Calculate or measure the total items in process.

**Next, determine the throughput.**Calculate the throughput of the system.

**Finally, calculate the lead time.**Calculate the lead times using the formula above.

## FAQ

**What is throughput?**

Throughput is a rate of production of goods within a system.