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Interactive Tools
System Design Calculators
Back-of-envelope calculations made easy. Plug in your numbers and get instant estimates for QPS, storage, bandwidth, cache sizing, server count, and system availability.
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QPS Calculator
579
Avg QPS
1,737
Peak QPS
1,579
Read QPS
158
Write QPS
Formula: Avg QPS = DAU × Requests/User / 86,400. Peak QPS = Avg QPS × Peak Factor.
💡 Interview Tips for Estimation
- 1.Round aggressively — 86,400 ≈ 100,000 is fine. Show you know the approach.
- 2.State your assumptions clearly. "I'll assume 10M DAU with 5 requests per user per day."
- 3.Calculate peak first, then design for 2-3× peak for headroom.
- 4.Don't forget replication factor (usually 3×) when sizing storage.
- 5.Use powers of 2 for quick math: 2¹⁰ ≈ 1K, 2²⁰ ≈ 1M, 2³⁰ ≈ 1B.
Want to practice estimation in context?
Our case studies start with real back-of-envelope calculations.