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Google·Software Engineer·Onsite - Product Sense / Strategy·Senior

SeniorPrefer not to say
May 2026

Summary

Interviewed for a PM role at Google and got hit with an estimation question about Gmail storage planning. Pretty classic product sense meets data reasoning combo, but the scale of Gmail makes it way less straightforward than it sounds.

Questions Asked (1)

Q1

You're the PM for Gmail. How would you figure out how much storage to purchase for the next year?

Product Analytics & MetricsProduct StrategyTechnical Trade-offs
Author's notes

I started with current user base and average storage per user, then tried to layer in growth projections and attachment trends.

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AI HintsAI Generated

Suggested Approach

Break the problem into demand (how much storage users will consume) and supply (how much storage Google needs to provision), then estimate each component using available data and reasonable assumptions. Structure your answer by first outlining a framework, then walking through the calculations with clear assumptions, and finally discussing trade-offs and risks.

Pro tip: Anchor your estimate to a familiar metric like daily active users (DAU) and average storage per user, and explicitly state that you'd validate assumptions with real data from Google's internal dashboards before finalizing the purchase.

1. Clarify the goal and scope

Confirm that the goal is to determine the total storage capacity to purchase for Gmail for the next year, considering growth, usage patterns, and redundancy. Ask clarifying questions about user base, growth rate, and existing storage infrastructure.

2. Estimate demand: current and future storage needs

Calculate current storage usage by estimating the number of Gmail users, average storage per user (including emails, attachments, and metadata), and then project growth over the next year based on user growth and increasing attachment sizes.

3. Account for supply-side factors

Consider factors like data redundancy (replication), backup requirements, compression, and storage efficiency improvements. Also factor in storage already owned and the lead time for procurement.

4. Compute the required purchase

Subtract existing available storage from the projected total demand to find the additional storage needed. Add a buffer for unexpected spikes or forecasting errors.

5. Validate and iterate

Discuss how you would validate assumptions with real data (e.g., historical growth rates, usage analytics) and adjust the estimate. Mention monitoring and adjusting the purchase plan as new data emerges.

Key Points to Mention

  • Number of Gmail users (e.g., 1.8 billion) and daily active users
  • Average storage per user (e.g., free tier 15 GB shared across Google services, but Gmail-specific usage)
  • Growth rate of users and storage per user (e.g., 5-10% annually)
  • Data redundancy and replication factor (e.g., 3x for durability)
  • Storage efficiency measures like compression and deduplication
  • Existing storage capacity and procurement lead times

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.