Summary
- Team wishing to enact improvements in their delivery performance can look to Little’s Law for guidance.
- WIP, Cycle Time, and Throughput are all Flow Metrics, and their relationship is described by Little’s Law.
- Both Scrum and Kanban teams can use these metrics to identify opportunities for improvement in their delivery performance.
At its core, Lean Improvement focuses on delivering maximum value to the customer. Every process, decision, and change is viewed through the lens of customer value. By focusing on refining processes and eliminating waste, organizations can deliver products and services that meet or exceed customer expectations. This means identifying what customers truly value—speed, cost, quality, predictability, flexibility—and ensuring that all improvement activities are focused on providing these benefits. Whether through faster delivery times, reduced costs, or higher quality, continuous improvement ensures that every change is made with the customer’s experience in mind.
An Agile production framework can be thought of as a system of delivery based on producing in small batches that are amenable to inspection and adaptation for the purpose of iterating towards an optimal solution.
The fundamental enablers of this approach are:
- Small, cross-functional teams with all skills needed to independently produce working software as the output of each sprint.
- Product Backlogs created in a way that enable incremental delivery and flexibility – user stories.
- A set of practices that support the ability to produce working software as the output of every sprint. This generally needs a level of CI and Test Automation in place as a supporting prerequisite.
New product capabilities or improvements are of zero value until they reach the hands of users. True value is realized when we get beyond ‘working/tested software’ to ‘working/tested/deployed’ software.
Cycle Time (or Lead Time) is the key metric, and Agile development teams seek to relentlessly improve it. Cycle Time measures the elapsed time between when work starts on a backlog item and when it is done. Little’s Law describes the factors that influence Cycle Time.
Little’s Law can be stated:
Cycle Time = Length of Input Queue (WIP)/Processing Rate (Throughput)
- WIP. The numerator in the equation is the amount of work in progress in the system. That is, the number of items started but not finished. This can be applied to the entire end-to-end process, or for any individual step within the process. Ideally we would have a maximum of one item queued, in which case we would have a one-piece-flow situation where only one piece of work was processed at a time. There would be no steps where work was delayed or waiting for work ahead of it to be processed. In this ideal case the amount of work in the system, WIP = 1. The numerator is Little’s Law can be heavily influenced by basic workflow design, team structures and work item variability – anything to minimize the build up of queues, buffering of work within the workflow. This is where change can be enacted fastest.
- Throughput. The denominator in the Little’s Law equation is the processing time per item or throughput of the system. The larger (faster) this value the shorter the Lead Time – common sense. This parameter can be improved in 2 ways:
- Remove non-value-adding work (waste) from the processing steps (all of the classic 7 sources of waste from Lean: fixing defects/re-work, over production, over processing, unfinished goods (WIP), non value-adding steps, and so on).
- Increase production capacity and speed: more equipment, more people, more automation, tooling improvements. These improvements are likely to take more time and more investment.
Here’s another way to think about it:
When deciding on any course of action to improve a process, for example as the outcome of a retrospective, it is worth considering how that action impacts either the numerator or denominator of Little’s Law. (If it affects neither it’s probably a waste of time).
Cycle Time is an example of a flow metric. Flow is a measure of how effective an organization is at delivering value. Relentless Improvement, one of the Lean principles, is focused on improving flow.
A Little’s Law Mindset is a Flow Mindset. Viewing every process, decision, or change through the lens of Little’s Law is seeing it through the lens of customer value. This is the Agile Mindset.
More on Flow Metrics here.