Kanban Card Calculator (How Many Kanbans for a Loop)
Number of kanban cards or containers needed to keep a production line supplied, from the demand, the replenishment lead time, a safety allowance and the container size.
Results
What this tool does
In a kanban system each card stands for one container of parts in circulation, so the number of cards caps the work in progress. During the replenishment lead time — everything from the card being released to full containers coming back — the line consumes demand × lead time pieces, plus a safety allowance for variation; dividing by the container size and rounding up gives the cards. Too many cards hide problems under stock, too few starve the line. Reducing the lead time, or the container size, is the lean way to cut the number of cards.
Formula
N = ⌈ demand × lead time × (1 + safety) ÷ container size ⌉
Variables
| Symbol | Meaning | Unit |
|---|---|---|
d | Demand per day (pieces) | pcs/day |
lt | Replenishment lead time (days, including transport and waiting) | days |
sf | Safety allowance | % |
cs | Pieces per container | pcs |
N | Number of kanban cards (containers) | — |
X | Containers needed before rounding up | — |
MX | Most pieces that can be in the loop | pcs |
CV | Days of demand the loop holds | days |
Worked example
- Demand per day (pieces)400 pcs/day
- Replenishment lead time (days, including transport and waiting)1.5 days
- Safety allowance20 %
- Pieces per container50 pcs
- Number of kanban cards (containers)15
- Containers needed before rounding up14.40
- Most pieces that can be in the loop750 pcs
- Days of demand the loop holds1.88 days
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.