Kanban controls production and replenishment based on actual consumption via visible signals with fixed rules — so the flow becomes self-governing, WIP is limited, and overproduction is structurally prevented.
Consumption per item is reasonably known and repeated (runners/regulars — not exotics)
The replenishment time is known and reasonably stable
The discipline agreement is in place: nothing is produced/ordered without a signal — not even “just in case”
Start with the runners: high, even consumption. Define the loop precisely: who consumes, who replenishes, where the stock sits. One loop at a time — kanban is rolled out loop by loop, not as a big bang.
The basic formula: coverage of consumption during the replenishment time + safety for variation. Number of kanban = (daily consumption × replenishment time in days × (1 + safety factor)) ÷ quantity per kanban. Round up, start deliberately a little generous — and reduce later: kanban is tightened gradually, which is how the system reveals problems in small doses.
A card, an empty bin, a marked floor place, a two-bin system or an electronic signal — choose the one that can’t be misunderstood or lost. The signal’s path must be defined: who picks it up, when, and where is it delivered?
The classic rules: (1) nothing is produced without a kanban, (2) produce only the quantity on the card, (3) defective parts are never passed on in the loop, (4) the kanban always follows the item. The rules hang at the loop and are trained with everyone involved.
The first 4-6 weeks are audited weekly: does the number of cards fit? Are the rules followed? Where do panic violations arise — and why? Violations are diagnoses: they point to unreliable replenishment or wrong sizing. Fix the cause, not the discipline.
When the loop runs stably: remove a card and see what happens. Problems that surface are solved — and then the next is removed. Inventory is a painkiller; kanban is the controlled tapering. Then the next item group.
How it goes wrong in practice — and this is where most implementations part ways.
If replenishment fails, people save themselves with shadow stocks — and the system is dead. The reliability of replenishment is the foundation; measure it first.
One accepted violation, and the rule no longer exists. Management must back the rules precisely when things heat up — that is when the system either sets or dies.
Consumption and replenishment times change; the card count must be revised regularly (e.g. quarterly). An outdated kanban system is just inventory with extra paperwork.
The method only works when it becomes daily routines and leadership behaviour. The operations check shows in 4 minutes where your operations stand — and what should come first.