VSM Studio
VSM guide / Lean tools / Kanban calculator
Kanban calculator
Size a pull system in seconds: how many kanban cards or containers you need, the maximum supermarket inventory and how many days it covers. Free, no sign-up.
The kanban formula
Number of kanbans = demand × (replenishment lead time + order interval) × (1 + safety factor) ÷ parts per container, rounded up.
Replenishment lead time
From the moment a container is emptied until it comes back full: the card's trip back, the wait in queue, changeover, run and transport.
Order interval
How often cards are collected or orders placed. A daily milk run adds a day; continuous pickup adds nothing.
Safety
Cover for demand swings and unreliable replenishment. Start at 10–30%, then lower it as the process stabilizes.
Containers
Smaller containers mean more cards but less inventory and faster signals. Two-bin systems need at least two.
Then take cards out
The first number is a starting point, not a target. Every card is inventory. Once the loop runs smoothly, remove a card at a time; when it hurts, you have found the next problem to fix (changeover, reliability, transport).
In the VSM Studio builder, size any inventory triangle as a supermarket, or add a sized supermarket after a process. The map's lead time and simulation update with the new maximum.
Questions
What is a supermarket in lean?
A controlled store of parts with a fixed maximum, placed where continuous flow is not possible. The downstream process takes what it needs; the upstream process makes only what was taken, signaled by kanban cards.
How many kanban cards do I need?
Use the formula above: demand times replenishment time (plus the order interval), plus a safety margin, divided by the container size, rounded up. The calculator shows the arithmetic.
What safety factor should I use?
Start between 10% and 30% depending on how much demand varies and how reliable replenishment is. Lower it as you fix the causes of variation.
Is this the same as a reorder point?
Close. A reorder point triggers at one stock level; kanban spreads the same logic over containers, so every empty container is a signal and inventory is visible on the floor.