1. A computer-implemented method for determining an optimal lot size for multiple items in a flow path, comprising: (a) receiving a selection of a lot size for each item in the flow path; (b) based at least in part on the selected lot sizes, estimating a respective cycle time for the items in the flow path; (c) based at least in part on the respective cycle times, determining an aggregate cycle time for the flow path, wherein the aggregate cycle time comprises at least one search direction; (d) based in part on at least the aggregate cycle time, determining whether to modify a lot size for a particular item to optimize the aggregate cycle time; and (e) if a determination is made to modify a lot size for a particular item, repeating elements (a)-(d) as needed by applying an iterative algorithm based in part on Powell's method.