> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/donnemartin/system-design-primer/llms.txt
> Use this file to discover all available pages before exploring further.

# 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](https://en.wikipedia.org/wiki/Power_of_two)
* [Use back of the envelope calculations](http://highscalability.com/blog/2011/1/26/google-pro-tip-use-back-of-the-envelope-calculations-to-choo.html)