I started from total US population and tried to work down by age, internet access, and email adoption rates.
Start by clarifying the scope: are we estimating total Gmail accounts or active users? Then use a top-down approach: estimate the US population, segment by age and internet usage, and apply adoption rates for email and Gmail specifically. Alternatively, use a bottom-up approach: estimate Google's overall user base and the proportion using Gmail.
Pro tip: Acknowledge that Gmail has both consumer and enterprise users; consider that many people have multiple Gmail accounts, so distinguish between accounts and unique users. Also, mention that you'd validate your estimate with known data points like Google's reported user numbers or third-party stats.
Ask whether we're estimating total Gmail accounts or active users, and whether we include enterprise (G Suite) users. This ensures you're solving the right problem.
Decide between top-down (population-based) or bottom-up (Google user base-based). For a PM interview, top-down is often more intuitive and easier to explain.
Break down the US population by age groups (e.g., under 13, 13-65, 65+) and apply internet and email usage rates. Consider that Gmail is popular among younger demographics.
Estimate the percentage of email users who use Gmail. Consider competition from Yahoo, Outlook, etc. Also factor in multiple accounts per user and enterprise usage.
Multiply the segments to get a total, then adjust for overlaps and multiple accounts. Compare with known benchmarks (e.g., Gmail has ~1.5B users globally, US is ~10% of that).
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.