How do target, effective, and local utilisation differ?

Short Answer

Target utilization is your input assumption going in; effective utilization is what actually got achieved after real exclusions (blockages, macros, halos) are accounted for; local utilization narrows the question to a specific smaller region instead of the whole block. These answer genuinely different questions, and comparing across them is meaningless unless you're using the same object classes, the same exclusions, and the same region definition each time.

Technical Explanation

• The city analogy is the clean way to remember it: a city can show plenty of open land in its overall statistics while one particular neighborhood is completely full — global utilization numbers can hide a local placement failure entirely.
• Blockages, voltage areas, halos, and fragmented rows are exactly the things that shrink usable capacity locally without moving the global number much at all.

Formula Or Decision Rule

Local utilisation = counted area inside region / usable placeable area inside the same region.

What To Check

• Warning sign: Average utilisation looks healthy while cells are trapped beside a macro or voltage-area boundary.
• Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause.
• Correct: Measure the failing region, remove the cause of fragmentation or redistribute demand, then recompute.

Healthy, Suspicious & Hard-stop Results

• Healthy: Target utilisation is an input assumption; effective utilisation is the achieved counted occupancy after exclusions; local utilisation measures a smaller region. They answer different questions.
• Hard stop: required legality or physical feasibility is missing or unexplained.

What The Interviewer Is Testing

” to measurable physical evidence and an owned correction.