Powers of Two Table

Quick reference table for powers of two, essential for back-of-the-envelope calculations in system design

You’ll sometimes be asked to do ‘back-of-the-envelope’ estimates in system design interviews. For example, you might need to determine how long it will take to generate 100 image thumbnails from disk or how much memory a data structure will take. The Powers of two table is a handy reference for these calculations.

Powers of Two Reference

Power	Exact Value	Approx Value	Bytes
7	128
8	256
10	1,024	1 thousand	1 KB
16	65,536		64 KB
20	1,048,576	1 million	1 MB
30	1,073,741,824	1 billion	1 GB
32	4,294,967,296		4 GB
40	1,099,511,627,776	1 trillion	1 TB

Usage in System Design

This table helps you quickly estimate:

• Memory requirements for data structures
• Storage capacity needed for different scales of data
• Network bandwidth calculations
• Cache sizing decisions

Further Reading

• Powers of two - Wikipedia
• Use back of the envelope calculations