Estimate Annual Data Traffic for a Top-Ranked Global Mobile Chat App
Company: Google
Role: Product Manager
Category: Product / Decision Making
Difficulty: medium
Interview Round: Other
Suppose you set out to build the mobile messaging app that becomes the most used in the world. Estimate how much network bandwidth the app would consume in one year.
Lay out the equation you would use, the assumption behind each input and the arithmetic, then finish with a figure, a range and a check that it is reasonable.
```hint Follow one active user's day
Estimate what a typical active user sends and receives in a day, broken down by content type, before scaling up. Ask yourself which types carry most of the bytes and which barely register.
```
### Clarifying Questions
- Does "bandwidth" mean the total volume of data moved over the year, or the peak throughput the network has to be built for?
- Whose traffic counts: only data that passes through the app's own servers, or everything the app uses on users' connections, including peer-to-peer calls?
- Which features are in scope: text, photos, videos, voice notes, voice and video calls, chat backups?
- Should the estimate assume the app has already reached the size of today's largest messaging apps, or cover its first year?
### What a Strong Answer Covers
- A definition of what is being measured (yearly volume or peak throughput) and of the traffic in scope
- A clear equation linking daily active users and per-user daily traffic to a yearly total
- Per-user traffic broken down by content type with plausible sizes, counting both sending and receiving, including delivery to group members
- Correct unit handling from kilobytes up to exabytes, a final range and a sanity check
- What drives the bytes, and how the estimate would shape infrastructure and cost decisions
### Follow-up Questions
- What peak throughput would the network need to handle, and how do you get there from your yearly figure?
- Which product decisions would cut traffic the most, and what would each cost users in experience?
- How does your estimate change if video calling grows from a side feature into the main way people use the app?
Overview: A product manager estimation prompt about the yearly network bandwidth of a mobile messaging app that has become the most used in the world. It tests setting up a clear equation, sizing per-user traffic by content type, accounting for group delivery and calls, and converting units correctly.