Overplanning factor in Toyota's formula for computing the number of kanban

To determine the number of required kanban, Toyota uses a formula based on the average demand during an order picking cycle, inflated by a constant overplanning factor β. This technical note attempts to characterize the situations where the simplicity of Toyota's formula reconciles with the established operations research paradigm of optimality. The overplanning policy examined in this paper could also be applied to other production inventory control models under uncertainty.