Recently a reader posed the following value-stream mapping, lead time-related question(s). My experience, after facilitating more value-stream mapping activities than I care to remember, is that it’s not an uncommon question. In fact, it’s a very good question.

I provided a quick answer, supplemented by the very sophisticated graphic in figure 1.

Q: Say you have a value-stream map that after Process A is complete, can either go to B, C, or D, and then no matter the process, continue to E from there. How do you go about adding up lead time? Do you just take the longest of those three times or an average?

A: In such a situation, lead time, as reflected on the “top rung” of the lead time ladder, is based on the inventory in the system. The lead time on each rung is typically calculated by dividing the average daily demand by the inventory count associated with the triangle (typically) above that rung. This will provide lead time in terms of days or fractions of a day. (There are other methods, but this one is probably the most simple.)

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