From DAU to QPS

What you take away

• The chain is always the same: DAU × actions per day = requests per day ÷ 86,400 = average QPS.
• Round 86,400 to 100,000 — you land within 16%, which is well inside the precision of the inputs.
• Size for peak, not average: a peak factor of 2–3× is typical, and event-driven traffic is far spikier.
• Split reads from writes before choosing anything: the ratio decides caches, replicas and shards.

How the class is laid out

1. The problem
2. The simple version
3. The chain
4. Check your understanding