Flow Formula Calculator
Interactive versions of the three formulas from Part 8 — Little's Law, Kingman's formula, and Weinberg's context-switching numbers. Plug in real numbers from an engagement to see what they predict.
Little's Law
L = λ × W
Work in progress equals arrival rate multiplied by average time in system. Give it any two values and it solves for the third. Keep the time unit for arrival rate and cycle time consistent — both in days, or both in weeks.
Result—
Kingman's formula (the VUT equation)
Wait ≈ V × U/(1−U) × T
Estimates average wait time from variability, utilization, and average processing time. The curve is not linear — watch what happens as utilization approaches 100%.
Estimated average wait—
Reading the curve: the last 10–15% of utilization is where nearly all the danger lives. Two teams at 65% and 90% utilization aren't "a bit different" — they're qualitatively different systems.
Weinberg's context-switching numbers
How much effective capacity a person loses as concurrent projects increase. A practitioner heuristic, not a lab measurement — but the most-cited figures in the field.
Effective capacity lost to switching—
Weinberg's data doesn't extend meaningfully past five concurrent items — the trend just keeps getting worse. The only real levers:reduce how many concurrent items that person is allowed to hold, or reduce genuine demand on them.
Want a guided walkthrough instead of raw formulas? Try theFlow & Constraint Diagnostic — or see these formulas applied to a full worked example in theFlow Deck.