Triangle kanban, while one of three types of signal kanban, are unique in that there is only a single kanban per part number or stock keeping unit. Accordingly, kanban sizing math has nothing to do with determining the number of kanban - that’s obviously fixed.
Instead, the math is around determining the total manufacturing lot size, which is the total kanban size, and the appropriate replenishment trigger point or re-order point. Re-order point is addressed in a separate entry by the same title.
There are two basic methods of sizing triangle kanbans. We will call these: 1) product specific lot size, and 2) universal lot size. The first applies a universal every part every interval (EPEI) for all parts made by the supplying operation. This yields lot sizes that are unique to each part because they are based upon their own unique demand. The second method applies EOQ-type thinking and/or a more simplistic one size fits all approach to determine a universal lot size for all parts. For example, management may determine that the supplying operation will produce every part number in 500 piece lots, no matter what each part number’s specific average demand level may be.
The product specific lot size method better matches production with demand and thus minimizes inventory levels, although it is a bit harder to manage. The universal lot size method, while easier to manage (same lot size for every part), will generally require more inventory.