System Process Time

System process time is the sum of all individual step process times in a serial process. It represents the best-case scenario, how long it would take to process one unit if there were zero queues, zero delays, and every step started immediately after the previous one finished.

System process time does not change when resource availability is reduced (the real work still takes the same time). However, the apparent system process time, accounting for availability, does increase.

Note on “Lead Time”: Some practitioners use lead time as a synonym for system process time, but more commonly lead time refers to the total elapsed time from order to delivery (equivalent to flow time). This glossary uses “system process time” to avoid confusion.

Formula

Tmin = Σ p₁ + p₂ + ... + pₙ

Example

A coffee shop order process: Take Order (1 min) + Make Drink (5 min) + Prepare Food (3 min) + Serve (1 min) = 10 minutes system process time.

In reality, during the morning rush a customer might wait 25 minutes from ordering to receiving their food (flow time), but only 10 minutes of actual work happens.

Why It Matters

The gap between system process time and flow time reveals how much delay exists in your process. If a unit takes 10 minutes of actual processing but 25 minutes of flow time, more than half that time is waiting. Closing this gap, through queue reduction, bottleneck improvement, or delay elimination, is where the biggest efficiency gains typically come from.