Work out kanban card quantity instantly with clear inputs, formula shown and shareable results.
Kanban card count is demand during lead time, uplifted for variability, divided by container size and rounded up. Each card authorises one container, so the card count is a hard cap on work-in-process: maximum inventory is cards x container quantity.
Kanban cards
Cards = ceil(daily demand x lead time x (1 + safety allowance) / container size)
Inventory cap
Maximum inventory = cards x container quantity
Remove a card. That forces lead time or container size down; if the line starves, the underlying constraint is exposed and can be fixed. This is the deliberate mechanism of continuous improvement in pull systems.
10-20% for stable internal loops with reliable supply, 30-50% for external suppliers or variable demand. Excessive allowance defeats the purpose of the pull system.