A GUID is a 128-bit value consisting of one group of 8 hexadecimal digits, followed by three groups of 4 hexadecimal digits each, followed by one group of 12 hexadecimal digits.

The following example GUID shows the groupings of hexadecimal digits in a GUID:

6A35C390-D0E4-403F-85C2-3593D7218AE9

While each generated GUID is not guaranteed to be unique, the total number of unique keys ** (2^128 or 3.4×10^38)** is so large that the probability of the same number being generated twice is very very small.

For example, consider the observable universe, which contains about __5×10^22__ stars, every star could then have about __6.8×10^15__ universally unique GUIDs.

There are 2^{128} possible GUIDs; that’s almost **40 Billion Billion Billion** unique GUIDs for every person on earth.

2^128 is exactly equal to

**340,282,366,920,938,463,463,374,607,431,768,211,456**

This is the total number of possible GUIDs in this universe.

A GUID is:

- 1 in 2^128
- 1 in 340 undecillion (see more here NUMBER TABLE)
- 1 in 3.4 × 10^38
- 1 in 340,000,000,000,000,000,000,000,000,000,000,000,000

Assume that we have __2 ^{30}__ computers and we put all these computers to the task of generating GUIDs, if each computer can generate, about

__2__GUIDs per second.

^{20}then after only about

__2__seconds —

^{72}**150 trillion years**,

you’ll have a

*very high*chance of generating a duplicate GUID.

With the above maths, it is very unlikely of getting a duplicated GUID, but still, we cannot say that GUID is Guaranteed Unique.

**Disclaimer:**

The above information might not be 100% accurate, it is just an estimation.