# Little's Law Calculator

> Relate work in process, throughput and lead time in a stable system.

Page: https://freecalculator.tech/tools/littles-law-calculator
Last reviewed: 2026-09-16

## Formula

WIP = Throughput × Lead time (so Lead time = WIP ÷ Throughput, and Throughput = WIP ÷ Lead time)

- WIP = Throughput × Lead time (so Lead time = WIP ÷ Throughput, and Throughput = WIP ÷ Lead time).
- Inputs used: What do you want to work out?, Average throughput, Average lead time, Average work in process.
- Edge handling: Average throughput cannot be negative.; Average throughput must be no more than 1000000000000.; Average lead time cannot be negative.; Average lead time must be no more than 1000000000000.; Average work in process cannot be negative..

## Inputs

- What do you want to work out?
- Average throughput
- Average lead time
- Average work in process

## Worked example: Work in process implied by a stable line

A line averaging 128 units an hour with a 3.5 hour lead time holds about 448 units between its start and end points.
1. Start with What do you want to work out?: wip, Average throughput: 128, Average lead time: 3.5, Average work in process: 0.
2. Apply the method: WIP = Throughput × Lead time (so Lead time = WIP ÷ Throughput, and Throughput = WIP ÷ Lead time).
3. A line averaging 128 units an hour with a 3.5 hour lead time holds about 448 units between its start and end points.

## Common questions

### Where does this formula come from?

MIT OpenCourseWare 2.854 Introduction to Manufacturing Systems — the published queueing result L = λW: for a stable system the average inventory equals the average throughput rate multiplied by the average time in system, whatever the arrival or service distributions. See the source link on this page.

### What kind of calculation is this?

For a stable system observed over a long enough window, the average number of items inside it equals the average arrival or departure rate multiplied by the average time an item spends inside. Check the formula, example, and limitations on this page before using the result for a real professional & industry decision.

### What are its limits?

Exact only for a stable system observed over a long enough window; for a short window, or while work in process is growing or draining, the three averages will not reconcile. It is a relationship between averages — it says nothing about the spread of individual lead times, or about why the work in process is what it is. Arithmetic over the figures entered — it cannot tell whether the measurements behind them are right. A measured result, an industry benchmark and an organisation's target are three different things; only the entered figures are used.

### How do I use the Little's Law Calculator?

Enter the required values for What do you want to work out?, Average throughput, Average lead time, Average work in process. The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.

### What formula does the Little's Law Calculator use?

WIP = Throughput × Lead time (so Lead time = WIP ÷ Throughput, and Throughput = WIP ÷ Lead time) The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone. Check the formula, example, and limitations on this page before using the result for a real professional & industry decision.

### Can the Little's Law Calculator be used for exact decisions?

Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.

## Limitations and assumptions

- Inputs outside the supported range are rejected rather than forced into a result.
- The result depends on the values you enter for this little's law calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.

## Sources

- Massachusetts Institute of Technology — https://ocw.mit.edu/courses/2-854-introduction-to-manufacturing-systems-fall-2016/

## Cite this page

- APA: Free Calculator. (2026, September 16). Little's Law Calculator. https://freecalculator.tech/tools/littles-law-calculator
- MLA: "Little's Law Calculator." Free Calculator, 16 Sept. 2026, https://freecalculator.tech/tools/littles-law-calculator.
- Link: Little's Law Calculator — Free Calculator, https://freecalculator.tech/tools/littles-law-calculator