Kanban Card Quantity Calculator

How it works

Kanbans = (daily demand × lead time × (1 + safety factor)) ÷ container quantity, rounded up (minimum 2); loop inventory = cards × container quantity

A kanban loop caps inventory between two process steps: each card (or bin) authorises one container of parts, and when a container is emptied its card travels back as the signal to replenish. The number of cards must cover the demand that occurs while a replenishment is in flight, plus a safety allowance for demand spikes and late deliveries; anything more is waste, anything less stops the line. Because the formula divides by container size, halving the bin roughly halves the inventory for the same protection — at the cost of more trips — which is why lean systems push for small, frequent containers and shorter replenishment loops rather than larger buffers. Recalculate whenever demand shifts by more than about 10%, and remove cards deliberately to expose problems.

Worked example

400 parts a day, a 1.5-day replenishment loop, bins of 50 and 20% safety: 400 × 1.5 × 1.2 ÷ 50 = 14.4 → 15 cards holding 750 parts (1.9 days, $6,000). Bins of 25 would need 29 cards but only 725 parts.

Frequently asked questions