Kanban Calculator
Size your kanban loop in seconds — the number of cards needed from demand, lead time, container size and safety. Free, instant and fully in your browser.
Kanban cards
24
cards (N)
N = ⌈ (D × LT × (1 + α)) / C ⌉
What is kanban card sizing?
A kanban system limits work in process by circulating a fixed number of cards, each authorising one container of parts. The card count must cover demand during the replenishment lead time, plus a safety buffer for variation. Too few cards starves the line; too many hide overproduction. The formula balances coverage against WIP.
How to size kanban cards
- 1
Demand during lead time
Multiply daily demand by replenishment lead time to find how much is consumed while you wait for resupply.
- 2
Add a safety factor
Increase by a safety factor (alpha) to absorb demand and supply variation — typically 10–30%.
- 3
Divide by container size
Divide by units per container and round up. That is your kanban card count, N.
Frequently asked questions
What safety factor should I use?
Start around 10–20% and adjust with observed variation. Stable, reliable supply and demand allow a smaller buffer; volatility needs more. Review it as conditions change rather than fixing it forever.
How does kanban relate to Little's Law?
Kanban caps WIP, and by Little's Law (lead time = WIP / throughput) capping WIP caps lead time for a given throughput. Sizing cards is, in effect, choosing your WIP limit.
When should I recalculate card counts?
Whenever demand, lead time, container size or variability shifts meaningfully. Pair it with standard work and balancing — measured in Yamazo Studio — so the loop reflects how the line actually runs.
Related lean tools & guides
Size the loop, then stabilise the flow
Cards cap WIP. Yamazo Studio turns shop-floor video into the standard work and balancing that keep throughput stable so the loop holds — one offline Lean Operating Desk.
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