Solve Little’s Law for WIP, throughput, or flow time with rate/time units, formula steps, shared-boundary checks, and batch-clearance context.

Use compatible long-run averages for the same process, population and system boundary. This does not predict an individual item’s waiting time.

Backlog clearance

Clearance assumes constant output capacity and no new arrivals.

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 long-run average throughput rate for the same defined system. In a balanced system, average arrivals and departures agree.
  • 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 compatible long-run average throughput and flow time for the same population and system boundary.

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 relates the average number of items in a defined system to its long-run average throughput and average flow time: L = λW. Use finite, compatible averages for the same population and system boundary; arrivals and departures can be used interchangeably when they balance over the observation basis.

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?

  1. First, determine the work in process.

    Calculate or measure the total items in process.

  2. Next, determine the throughput.

    Calculate the throughput of the system.

  3. 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.