System Design Refresher : Back-of-the-Envelope Calculations

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Back-of-the-envelope calculations offer a swift and practical approach to tackling system design challenges. Whether you’re estimating server capacity or calculating storage needs, these straightforward estimations can provide crucial insights that help guide your design decisions without getting bogged down in details.

To start with, here’s a quick cheat sheet to keep in mind as you perform back-of-the-envelope calculations for system design:

Few more quick references -

• 1 million(10⁶) = 1 million requests/day = 12 requests/sec (round off)
• char — 1 byte(ASCII), 2 byte(UNICODE)
• int32–4 byte, int64–8 byte
• float — 4 byte, double — 8 byte
• long — 8 byte

Now let’s consider a real time scenario/requirement and conduct a preliminary calculation for our back-of-the-envelope estimation.

Note: We’ll round off some results for simplicity and efficiency, enabling us to focus on key insights without getting caught up in exact figures.