Netflix System Design: Capacity Estimation
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Interview tip
Give order-of-magnitude estimates. Interviewers want reasoning, not precision.
How to present this in an interview
- 1.Start with bandwidth — it's the most impressive anchor number (45 Tbps = 15% of global internet).
- 2.Derive from DAU, not from thin air. Show your reasoning step by step.
- 3.Interviewers want order of magnitude, not precision. 260K RPS is fine; 261,574 is overthinking.
- 4.For each number, say what it implies for architecture (e.g. 500K events/sec → need Kafka, not SQS).
- 5.Always state your assumptions explicitly so the interviewer can correct them.
Capacity Estimation
The numbers interviewers expect you to derive on a whiteboard. Start with bandwidth — it's the anchor.
300M
users
Total subscribers
150M
DAU
Daily Active Users (50%)
15M
concurrent
Peak concurrent viewers
45
Tbps
Peak video bandwidth
260K
RPS
Peak API requests/sec
500K
events/sec
Peak Kafka/Kinesis events
Interactive Calculator
Adjust scale to see derived numbers
300M
50%
3 Mbps
DAU
150,000,000
Peak Concurrent
15,000,000
Peak Bandwidth
45.0 Tbps
Peak API RPS
260,418
Kafka events/sec
500,000
Cassandra (90d)
7,544 GB
Step-by-Step Derivations
Click any row to see the full derivation with assumptions and interview tips.