# Estimating QPS from daily users in three steps

- Source: https://intervueclub.com/blog/estimate-qps-in-three-steps
- Author: Anubhav Sethi
- Published: 2026-09-28
- Tags: estimation, interviews

Turn "10 million daily users" into requests per second, peak load and a machine count, with the arithmetic shown.

Most capacity questions start with **a user count** and end with **a number of machines**. The steps in between are short once you have done them a few times.

## Step 1: requests per day

Say the hypothetical app has **10 million daily users**, and each one opens the feed **20 times a day**. That's 10,000,000 × 20 = **200 million feed requests a day**.

## Step 2: average and peak per second

A day has 86,400 seconds, so the average is 200,000,000 / 86,400 ≈ **2,300 requests a second**. Traffic isn't flat; assume the busiest hour runs at **three times the average**, which gives about **7,000 a second**.

## Step 3: machines

If one API server handles **1,000 feed requests a second**, the peak needs 7 servers. Add one so a deploy or a failure doesn't push the rest past their limit: **8 servers**.

The [back-of-the-envelope math](/course/back-of-the-envelope-math) lesson works through the same method with storage and bandwidth.