Kanban Calculator
This kanban calculator works out how many kanban cards, and so how many containers, a pull loop needs. Enter average daily demand, the replenishment lead time, a safety factor and the quantity in each container.
Kanban cards needed
22
21.12 before rounding up
- Lead-time cover
- 19.2
- Safety
- 1.92
- Max in loop
- 1,100
22 cards of 50 hold up to 1,100 units, about 2.3 days of demand.
- Covers demand during the lead time: 19
- Safety buffer: 2
- Rounding up to a whole card: 1
Card counts per group are rounded for the picture; the total is the number above.
Example values are filled in. Replace them with your own; nothing you type leaves your browser.
Worked example
The example values, step by step
- Step 1 · Demand during lead time
480 units a day × 2 days
= 960 units
- Step 2 · Add safety
960 × (1 + 10%)
= 1,056 units
- Step 3 · Containers
1,056 ÷ 50 units
= 21.12
- Step 4 · Kanban cards
Round 21.12 up
= 22 cards
- Step 5 · Maximum in loop
22 × 50 units
= 1,100 units
Reading the result
In the example, an assembly line uses 480 brackets a day and the machining cell takes two days to refill an empty bin. Nineteen to twenty cards cover demand during that lead time, about two more are the safety buffer, and rounding up adds the rest.
The 22 cards cap the loop at 1,100 brackets, about 2.3 days of demand. Cutting the lead time to one day would roughly halve the cards and the inventory.
| Lead time | Before rounding | Cards | Maximum units |
|---|---|---|---|
| 0.5 days | 5.28 | 6 | 300 |
| 1 day | 10.56 | 11 | 550 |
| 2 days | 21.12 | 22 | 1,100 |
| 3 days | 31.68 | 32 | 1,600 |
Computed with the same formula as the calculator.
Common data mistakes
- Using peak demand instead of average demand plus a safety factor, which bakes extra inventory into every card.
- Measuring lead time as the supplier's machine time only, without the time a card waits to be collected and the bin waits to be delivered.
- Never recalculating when demand or lead time changes.
- Adding cards to cover a problem, such as late deliveries, instead of fixing it.
The methods behind the number
The formula
How it's calculated
- Number of kanbans
- Demand × Lead time × (1 + Safety factor) ÷ Container quantity
- Round
- Always up to the next whole card
- Maximum inventory
- Number of kanbans × Container quantity
The cards set a ceiling on inventory
Each card authorizes one container. The number of cards caps how much can sit in the loop, so setting it is a deliberate inventory decision as well as a calculation.
Start with what you have, then remove cards
Many teams set the first count with this formula, then take cards out one at a time while watching for shortages. Each removal exposes the next problem to fix.
Recalculate when demand changes
The count is only right for the demand and lead time you entered. Review it on a regular cycle, such as monthly, or when demand moves noticeably.
Frequently asked questions
How do you calculate the number of kanban cards?
What is a kanban card system?
What safety factor should I use?
What is the difference between a kanban card and a two-bin system?
Does the kanban formula work for e-kanban?
Sources and further reading
- Lean Enterprise Institute lexicon: kanban ↗
- Lean Enterprise Institute lexicon: supermarket ↗
- Taiichi Ohno, Toyota Production System: Beyond Large-Scale Production (book)
For vendors
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