Cianplan

Level 1: Foundations · L1.4 Back-of-the-envelope estimation & numbers to know

Latency numbers that matter in 2026

Recall orders of magnitude from memory reads to cross-region round trips.

12 min · Free

What you take away

  • Four anchors carry everything: RAM ~100 ns, SSD read ~100 µs, same-zone round trip ~100 µs, cross-region 60–160 ms.
  • Remember the ratios, not the digits: each anchor is about 1,000× the one above it.
  • You use these to rule designs out in seconds, not to predict performance.
  • Anything you cannot place within 10× of the right rung will be wrong by more than the design decision can absorb.

How the class is laid out

  1. The problem
  2. The four anchors
  3. Write it from memory