Stage 1 · Lesson 4 of 10
Back-of-the-envelope capacity estimates
Rough numbers turn a vague requirement into design decisions. This is . Start from users and what they do.
Say 10 million daily users each post 2 photos a day. That is 20 million uploads a day, or about 230 per second on average and perhaps 1,000 at peak. At 2 MB per photo, that is 40 TB of new storage every day.
That rules out keeping images in the database. It points to , a service built for large files, and a . Use round numbers: a day is about 100,000 seconds.
Keep units visible and state every assumption. The goal is the right (roughly the right number of zeros), not precision.
Common trapdoing the arithmetic and then never using it: every estimate should end in a decision, such as "this fits on one machine" or "this needs sharding".
A question to check yourself, an AI practice session and 2 cheat sheet entries come with the full roadmap. Unlock
Resources for this stage
Start with· follow one of these
- CoursePaidGrokking System Design Fundamentals
Design Gurus · Beginner · Subscription
Load balancing, API gateway, proxies, caching, CAP and Bloom filters: week 1 of the plan in order
- GitHub repoFreeThe System Design Primer
Donne Martin · Intermediate
Free: its scalability, latency, availability, CDN, load balancer and cache sections
Keep handy
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