Kanban Card & Container Sizing Calculator
Use average demand, the complete replenishment delay, a planning buffer, and fixed container capacity to size a Kanban loop. The result shows the whole number of cards to authorize and the quantity that those cards permit in the loop.
Required Kanban cards and containers20
- Total replenishment lead time
- 1.75
- Demand during lead time
- 875
- Safety allowance
- 87.5
- Unrounded Kanban requirement
- 19.25
- Authorized loop quantity
- 1,000
- Container-rounding surplus
- 37.5
- Authorized inventory coverage (working days)
- 2
All demand and lead-time inputs must use the same working-day basis.
How to use this calculator
- Enter average daily demand using the same working-day basis as every lead-time input.
- Add production, transport, and signal-collection delays that occur before a container returns to use.
- Choose a safety factor that reflects ordinary variation in demand and replenishment.
- Enter the fixed units per container, then use the whole-card result to set the authorized loop.
How Kanban card sizing is calculated
A fixed-container Kanban loop authorizes a defined number of containers to circulate between the supplying process and the point of use. Each card stands for one full container. The loop must cover expected consumption while a used container is signaled, replenished, and returned, plus a deliberate allowance for routine variation.
The calculator first combines the delays into total replenishment lead time:
L = Lp + Lt + Ls
It then calculates lead-time demand and the buffered requirement:
B = D × L
A = B × (s ÷ 100)
Q = B × (1 + s ÷ 100)
- D is average daily demand.
- Lp, Lt, and Ls are production, transport, and signal delays in working days.
- B is demand during lead time, A is the safety allowance, and s is the safety factor in percent.
With C units per container, the exact card requirement is K = Q ÷ C. Physical cards cannot be fractional, so the authorized count is always rounded upward: N = ceil(K). The authorized loop quantity is I = N × C. The difference I − Q is the inventory added solely by rounding to whole containers. When demand is greater than zero, coverage is V = I ÷ D working days.
What moves the result most
Demand and total lead time change the base requirement in direct proportion: doubling either doubles lead-time demand. Measure the full elapsed loop, not only machine run time. Waiting for a pickup, a card collection interval, order release, queue time, transport, and receiving can all belong in the lead time if they delay the next usable container.
The safety factor is a planning buffer, not a service-level calculation. It increases every card requirement after lead-time demand is calculated. Container capacity also has a practical effect: a larger container may reduce the number of cards, but its upward rounding can create more excess material. Review the rounding surplus alongside the card count when selecting a container size.
What this calculator leaves out
This is a fixed-container estimate based on average demand. It does not model setup constraints, minimum production batches, scrap, yield loss, supplier calendars, demand seasonality, container losses, or statistical variation in detail. Authorized loop quantity can be in production, transport, supermarkets, or at the point of use; it is not necessarily the physical on-hand balance at one location. Confirm the loop at the gemba and reduce excess cards only after the replenishment process is stable.
Worked example
Suppose average demand is 500 units per working day. Production lead time is 1 day, transport is 0.5 day, signal collection is 0.25 day, the safety factor is 10%, and each container holds 50 units.
Total lead time is 1.75 days, so lead-time demand is 500 × 1.75 = 875 units. The safety allowance is 875 × 10% = 87.5 units, making the buffered requirement 962.5 units. Dividing by 50 gives 19.25 cards, which rounds up to 20 cards. The authorized loop is 20 × 50 = 1,000 units, with 37.5 units of container-rounding surplus and 2 working days of authorized coverage.
Common questions
How many Kanban cards do I need?
Divide buffered lead-time demand by the fixed units per container, then round the result upward to a whole card. The upward rounding is necessary because a partial card cannot authorize a partial standard container.
What lead times belong in a Kanban calculation?
Include every elapsed delay from consuming a container until a full replacement is available at the point of use. That commonly includes card collection or order release, production queue and processing time, transport, and receiving or put-away delays.
Why are Kanban cards always rounded up?
Each card normally represents one complete container, so the calculated requirement must be converted to a whole number of containers. Rounding down can leave the loop short before replenishment arrives; rounding up creates the reported surplus instead.
What safety factor should a Kanban system use?
Choose a factor from observed demand and replenishment variation, then revisit it as the process improves. A percentage buffer is a practical planning choice, not a statistical promise of a particular service level.
Is authorized loop quantity the same as on-hand inventory?
No. Authorized loop quantity is the total material permitted by all active cards, which may be distributed across production, transport, supermarkets, and points of use. The on-hand balance at any one location can be much lower or higher at a given moment.
When should Kanban quantities be recalculated?
Recalculate when demand, lead time, container capacity, route design, or process reliability changes materially. Review the actual loop after a change rather than treating the initial card count as permanent.