Practice the underlying steps repeatedly: define the market, choose a sensible approach, make transparent assumptions, calculate accurately, and sanity-check the result.

Memorizing finished market-sizing examples can make you faster on familiar questions but does not necessarily improve your ability to build an estimate from scratch.

For one prompt, try both top-down and bottom-up approaches and compare them. Then ask which assumptions drive the answer most and whether the final number passes a basic reality check.

Use short daily drills and review the assumption logic as carefully as the arithmetic. Keep a list of useful reference numbers, but focus on being able to explain where every assumption comes from. Keep a short note of what improved and what still broke so the next practice session has a clear purpose. Related CaseBasix guide: https://www.casebasix.com/pages/case-interview