What is the maximum size of a cookie, and how many can be stored in a browser for each web site?

Question

I am learning about cookies, and I wonder about browser support:

• For each domain/web site, how many cookies may be sent to a browser, and of what size?

• If multiple cookies are sent and stored, does that affect performance?

Answer 1

Different browsers have different size limits on cookies. Some general guidelines:

Most of the documentation I've found (and there isn’t much) suggests that web browsers must support a minimum of:

• 300 cookies in total
• 20 cookies per domain
• 4096 bytes per cookie

It seems as though this minimum requirement is part of the original RFC for cookies – see section 6.3 specifically.

A page that lists the actual in-practice cookie limits for several browsers:

Per Domain Cookie Limit

Here is a test script to test your browser:

• Firefox 2: 50¹
• Firefox 3: 50¹
• Internet Explorer 7²: 50 (after applying a patch from Microsoft)
• Opera 9: 30
• Safari: No Limit(!)

Maximum Cookie Limit:

• Firefox 2: 1000¹
• Firefox 3: 1000¹
• Internet Explorer: unknown
• Opera: unknown

¹ can be set between 0 and 65535
² documented by Microsoft here

Cookies are not saved on a server basis but on a domain basis (a server may host many domains or the opposite a server farm may be serving a single domain).

In general, I would avoid saving lots of information in cookies, as the data gets sent to and from the browser on every request. As you suggest in your question, this can have a effect on performance.

Usually one stores small amounts of data in the cookie, mostly used to identify the user/session so more data can be picked up from a database or another resource local to the web server.