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Little's Law Calculator

Little's Law links three flow metrics: work in progress, throughput and cycle time. Enter any two and the calculator finds the third, then shows what happens to cycle time if you cut work in progress.

Solve for

Average cycle time

5 weeks

That is about 25 working days per item.

What if we cut WIP by 50%?

WIP30 → 15 items

Cycle time5 → 2.5 weeks

Assumes throughput stays the same.

Same throughput, less waitingEach dot is one item in progress.

Now

5 weeks30 items

WIP cut 50%

2.5 weeks15 items

Example values are filled in. Replace them with your own; nothing you type leaves your browser.

Worked example

The example values, step by step

  1. Step 1 · Work in progress

    Items started but not finished

    = 30 items

  2. Step 2 · Throughput

    Items finished per week

    = 6 a week

  3. Step 3 · Average cycle time

    30 ÷ 6

    = 5 weeks

Reading the result

In the example, an item started today will take about five weeks to finish on average. At a five-day working week, that is about 25 working days.

If throughput holds, cutting work in progress to 15 items would halve average cycle time to about two and a half weeks. In practice the effect is smaller if the system is unstable.

Common data mistakes

  • Mixing time units, such as throughput per week with cycle time in days.
  • Using a one-day snapshot of WIP instead of an average over the period.
  • Applying the law to a system that is growing or shrinking fast, where its averages do not hold.

The methods behind the number

The formula

How it's calculated

Cycle time
Work in progress ÷ Throughput
Work in progress
Throughput × Cycle time
Throughput
Work in progress ÷ Cycle time

Why limiting WIP works

If throughput stays the same, halving work in progress halves the average cycle time. That is the arithmetic behind WIP limits on a kanban board.

Use consistent units

If throughput is items per week, cycle time comes out in weeks. Mixing days and weeks is the most common mistake.

It works on averages

Little's Law describes long-run averages in a reasonably stable system. Use it to understand the system and set policies. It cannot give a reliable date for a single item.

Frequently asked questions

Does Little's Law apply to software teams?
Yes. It applies to any stable system where items arrive, wait and leave, including factories, hospitals, software teams and support teams.
What if our system is not stable?
The relationship still guides decisions, but the numbers will be less precise. Stabilize first: limit WIP and finish old items before starting new ones.
How do I forecast a single item?
Use the cycle time distribution from your historical data, such as the 85th percentile, rather than the average from Little's Law.
What is the Little's Law formula?
Average WIP equals average throughput multiplied by average cycle time. Rearranged, cycle time equals WIP divided by throughput.
When does Little's Law hold?
It describes long-run averages in a stable system, where work arrives and leaves at about the same rate. Count WIP, throughput and cycle time inside the same boundaries.
Can I use Little's Law to set WIP limits?
It helps you see the trade-off. Lower WIP means shorter cycle time if throughput holds, so teams often lower limits step by step and watch the result.

Sources and further reading

For vendors

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