Calculators

The arithmetic behind a system design answer, done live: change an input and every number updates. Each tool shows its formulas, gives you sentences to say out loud, and keeps its inputs in the link so you can share a result.

Everything runs in your browser. Nothing you type is sent anywhere.

Back-of-the-envelope calculator
Turn daily users, actions and payload sizes into average and peak QPS, storage per day and year with replication, and bandwidth in and out.
Latency budget planner
Build a request path from network hops, disk reads, caches and queries, group calls in sequence or in parallel, and see what is left of a p99 target.
Availability and SLO calculator
Combine components in series and in parallel, get overall availability, downtime per month and year, error budget minutes and SLO burn rate.
Sharding planner
From data size, growth, read and write rates and per-node limits, work out shards and replicas now and at your horizon, and when you will need to reshard.
Cloud cost estimator
A rough monthly bill from instances, storage, egress and requests, with editable illustrative unit prices, so you can say which line dominates.
Latency numbers to know
The classic table of cache, memory, disk and network latencies, as raw values or scaled to human time, with the orders of magnitude that matter in an estimate.