Back-of-the-Envelope Numbers Every System Designer Should Know

Tue, 05 May 2026 22:52:48 -0400

When you’re sketching a system architecture on a whiteboard, you don’t need precise benchmarks — you need to know whether your design is within an order of magnitude of feasible. Is one Postgres node enough? Do you need Kafka, or will RabbitMQ do? Should you reach for Cassandra, or is your workload nowhere near needing it?

Here are the numbers I keep in my head, calibrated against published benchmarks from Confluent, Instaclustr, Honeycomb, and others. Treat them as starting points for capacity planning, not SLAs.

System on Yiwei Shi

Back-of-the-Envelope Numbers Every System Designer Should Know