What is the length of a PHP session id string?

Question

I\'m making a table in a MySQL database to save some session data, including session_id. What should be the length of the VARCHAR to store the

Answer 1

@sachleen answer isn't full.
More detailed info about session id length is described here.

Summary:

128-bit digest (MD5)  
4 bits/char: 32 char SID    
5 bits/char: 26 char SID    
6 bits/char: 22 char SID

160-bit digest (SHA-1)
4 bits/char: 40 char SID    
5 bits/char: 32 char SID    
6 bits/char: 27 char SID

And sample regex to check session id:

preg_match('/^[a-zA-Z0-9,-]{22,40}$/', $sessionId)