Most candidates finish a market-sizing number and move on. Interviewers wait for the check: does this magnitude make sense for the market you just described?

A clean calculate with a wild final number still loses trust. Build a 15-second sanity check into every sizing.

The 15-second sanity stack

1. Order of magnitude: say the unit out loud (people, dollars, units per year). If you meant millions and said billions, stop.
2. Anchor: compare to one known base (US population, a category you know, a company revenue you just used).
3. Bound: give a low and high that still feel plausible, then land in the middle with a so-what.
4. Decision: fact, meaning, what you would do next if the true number is at the low end.

30-second script

"I get roughly 40 million units a year. US population is about 330 million, so that is roughly one in eight people buying once a year, which feels high for a niche product. I would use 15 to 20 million as the working case and keep price as the lever."

Want timed calculate and market-sizing drills with feedback? Start free (3 drills every week): casecrunchai.com

Drill it this week

• Set a 4-minute timer on one market-sizing prompt.
• Calculate out loud in chunks.
• Spend the last 30 seconds only on the sanity stack before your recommendation.

If you never check the magnitude, you are practicing speed, not judgment.

Drill free (3 drills every week): Start practicing free