Estimation — Netflix#

See 03-Streaming-Concepts.md for a full explanation of bitrate, bandwidth, throughput and latency in streaming vs non-streaming systems.

For bandwidth estimation we use 25 Mbps per stream as the worst case (all users on 4K). In reality the average is closer to 5–8 Mbps since most users watch at 1080p or below.

Assumptions#

300M MAU
50% DAU → 150M DAU
Average watch time per user per day = 1 hour
Peak multiplier = 3x average
20,000 titles total (movies + TV series)

Concurrent Viewers#

150M DAU watch 1 hour out of 24 hours

Average concurrent viewers = 150M × (1/24) = 6.25M
Peak concurrent viewers    = 6.25M × 3     = ~20M

Bandwidth#

Worst case bitrate = 25 Mbps per stream (4K)
Peak bandwidth     = 20M × 25 Mbps
                   = 500,000,000 Mbps
                   = 500,000 Gbps
                   = 500 Tbps

Why this number matters

500 Tbps cannot be served from a single data center — a standard server NIC maxes out at 10 Gbps. This single number justifies Netflix's entire CDN strategy — Open Connect, their in-house CDN with thousands of servers placed directly inside ISP networks globally.

Storage#

Content Storage#

Each title is stored in multiple resolutions and codecs — 4K, 1080p, 720p, 480p across H.264, H.265, and AV1. Combined, one title takes roughly 100 GB.

40% movies  → 8,000 titles  × 100 GB              =   800,000 GB =  0.8 PB
60% series  → 12,000 series × 50 episodes × 100 GB = 60,000,000 GB = 60.0 PB

Total content storage ≈ 64 PB

64 PB is chosen as the nearest power of 2 — clean for back-of-envelope math.

Metadata Storage#

Each title carries title, description, cast, director, genre, S3 URLs — roughly 1 KB per title.

20,000 titles × 1 KB = 20 MB — negligible

Metadata storage is irrelevant at this scale. The problem is entirely content storage and bandwidth.

Summary#

Metric	Value
Peak concurrent viewers	~20M
Peak bandwidth	~500 Tbps
Total content storage	~64 PB
Metadata storage	~20 MB (negligible)