About the Kanban Card Calculator
This kanban calculator applies the classic card-count formula used in lean manufacturing and pull-based replenishment: the number of kanbans equals the demand during the replenishment lead time, inflated by a safety factor, divided by the quantity in one container. It tells you how many cards (or bins) to put into circulation so the supplying process can keep up without starving the line.
It is meant for production planners, materials handlers and continuous-improvement teams setting up a new supermarket, two-bin system or supplier kanban, and for re-sizing an existing loop when demand or lead time changes. Lead time should include everything between a card being released and the full container arriving back: waiting for the card to be collected, queue time, processing or supplier time and transport.
The result is always rounded up to whole cards, because a fractional card does not exist and rounding down would leave the loop short. The calculator also shows the maximum inventory the loop can hold and how many days of demand that represents, so you can check the loop is not hiding excess stock.
With the default inputs, the kanban cards needed is 22. Change any value above to recalculate instantly.
How to use the kanban card calculator
- 1Enter average demand for the part in units per day.
- 2Enter the full replenishment lead time in days, including card collection and transport.
- 3Choose a safety factor — start around 10% and lower it as the process stabilises.
- 4Enter how many units one container or card represents.
- 5Read the number of cards to circulate and check the loop inventory and days of cover.
Formula and method
The number of kanbans N is the demand that occurs while one container is being replenished (average demand D × lead time L), increased by a safety factor S, and divided by the quantity each card authorises (container size C). The result is rounded up to the next whole card because a loop cannot run on a fraction of a card.
Lead time must be in the same time unit as demand — if demand is per day, lead time is in days. The maximum inventory in the loop is N × C; dividing it by daily demand gives the days of cover the loop represents. Reducing lead time or container size is the lean way to cut inventory without adding risk.
- N
- Number of kanban cards (containers) in the loop
- D
- Average demand per time unit (e.g. units per day)
- L
- Replenishment lead time, in the same time unit
- S
- Safety factor as a decimal (10% = 0.10)
- C
- Units per container (quantity per card)
Worked examples
500 units/day, 2-day lead time, bins of 50
Demand during the 2-day lead time is 1,000 units. Adding a 10% safety factor gives 1,100 units, and 1,100 ÷ 50 per container = exactly 22 cards. The loop holds at most 1,100 units, or 2.2 days of demand.
Low-volume part with a 20% buffer
120 units/day × 1.5 days = 180 units of lead-time demand; × 1.2 = 216 units; ÷ 25 = 8.64 cards, rounded up to 9. Nine totes of 25 hold 225 units, about 1.9 days of demand.
High-runner replenished every quarter day
A 6-hour lead time is 0.25 of a day, so lead-time demand is 600 units. With 15% safety that becomes 690 units, or 17.25 containers of 40 — rounded up to 18 cards holding 720 units (0.3 days).
Frequently asked questions
What is the formula for the number of kanbans?+
Number of kanbans = (average demand × lead time × (1 + safety factor)) ÷ container quantity, rounded up. Demand and lead time must use the same time unit, such as units per day and days.
What should be included in kanban lead time?+
Everything from the moment a container is emptied until a full one is back at the point of use: time for the card to be collected, waiting in the queue, setup and processing (or supplier lead time), and transport back to the line.
How big should the safety factor be?+
Many plants start with 10%–20% while a loop is new or demand is volatile, then reduce it as variation is understood. A high safety factor hides problems, so lean practice is to lower it gradually and fix the causes of stockouts.
Why is the card count always rounded up?+
Cards and containers are whole items, and rounding down would give the loop less capacity than the calculated lead-time demand, which risks stopping the downstream process.
How do I reduce the number of kanban cards?+
Shorten the replenishment lead time (faster changeovers, more frequent pickups) or reduce demand variability so a lower safety factor is safe — both cut cards and inventory. Larger containers also mean fewer cards, but they raise loop inventory; smaller containers do the opposite (more cards, less stock).