Little's Law Calculator (WIP, Throughput, Lead Time)
Lead time, work in progress or throughput of any process from the other two, by Little's law — fill in the two you know.
Results
Lead time (days each item spends inside)
5.00
d
Work in progress (items in the system)
—
Throughput (items finished per day)
—
/d
What this tool does
Little's law says that, on average, the number of items in a process equals the rate at which they come out times the time each spends inside. It holds for almost any stable system — a kitchen, a support queue, a warehouse, a software team — with no assumptions about how work arrives. Its practical message is uncomfortable but useful: if throughput stays the same, the only way to cut lead time is to have less work in progress, which is why Kanban limits WIP instead of pushing more work in.
Formula
WIP = throughput × lead time (fill in any two)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
wip | Work in progress (items in the system) | — |
th | Throughput (items finished per day) | /d |
lt | Lead time (days each item spends inside) | d |
LT | Lead time (days each item spends inside) | d |
WIP | Work in progress (items in the system) | — |
TH | Throughput (items finished per day) | /d |
Worked example
- Work in progress (items in the system)60
- Throughput (items finished per day)12 /d
- Lead time (days each item spends inside)5.00 d
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.