Numbers Every Engineer Should Know

You don't need to memorize a giant spreadsheet of numbers. But having a few key reference points in your head makes capacity estimation dramatically faster and more credible. This lesson gives you the numbers that matter most, the ones that change design decisions.

The questions that send you looking for them sound like design questions and are really arithmetic: does this need a cache, can one database hold a year of writes. Answering either one takes a multiplication, and the numbers below are what you multiply. Without them, the strongest thing you can say is "that seems like a lot," which is the weakest sentence available to you in a design round.

A rough figure you can defend beats a confident guess every time, and what makes it defensible is the multiplication you did out loud on the way there. Put ~10ms on a database query and 100K seconds in a day, and most sizing questions collapse into one multiplication and one division you can do while you talk.