Numbers to Know

In system design interviews, you'll estimate storage requirements, bandwidth needs, and whether a particular architecture can handle the load. Having the right numbers in your head—and knowing how to use them—separates candidates who can design real systems from those who memorize patterns.

One of the biggest red flags is when candidates propose complex solutions based on outdated assumptions. They worry about database sizes that modern instances handle easily, or suggest sharding for workloads a single server manages comfortably. Many textbooks and courses teach numbers from 2015 or earlier—hardware has improved dramatically since then.

This page covers the essential numbers for 2026 and teaches you how to apply them in back-of-envelope calculations.