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System Design Capacity & QPS Calculator
Estimate QPS, peak throughput, multi-year disk storage, bandwidth, and in-memory cache working sets in under two minutes for your system design interview.
Load Archetype:
Input System Parameters
50,000,000
20
2 KB
Calculated Architectural Metrics
Throughput QPS
11,574 avg
Peak: ~23,148 QPS (2x)
Read: 10,522 • Write: 1,052 QPS
Total Daily Requests
1000.0M / day
Across 50,000,000 daily active users
Storage Growth
173.4 GB / day
5-Year Total: 309.0 TB
In-Memory Cache (80/20)
346.8 GB RAM
Caches 20% of daily read requests in Redis
Network Bandwidth Egress172.39 Mbps
Network Ingress17.24 Mbps
Annual Storage61.81 TB / yr
Back-of-the-Envelope Mental Math Rules
- • 86,400 seconds in a day: Round to 100,000 (10^5) seconds for fast mental math in interview whiteboards.
- • 1 Million requests / day ≈ 12 QPS: A system handling 100M requests daily has an average throughput of ~1,200 QPS.
- • Peak traffic is typically 2x to 3x: Always calculate peak QPS to provision autoscaling server groups and connection pool maximums.
- • 80/20 Pareto caching principle: 80% of read traffic accesses 20% of data. Cache that 20% working set in memory to absorb database read spikes.