In an application I was developing I ran into what appeared to be a POST limit of about 2KB. It turned out to be that I was accidentally encoding the parameters into the URL instead of passing them in the body. So if you're running into a problem there, there is definitely a very small limit on the size of POST data you can send encoded into the URL.
Quite amazing how all answers talk about IIS, as if that were the only web server that mattered. Even back in 2010 when the question was asked, Apache had between 60% and 70% of the market share. Anyway,
min(serverMaximumSize, clientMaximumSize)
.Here are the POST body sizes for some of the more popular HTTP servers:
HTTP may not have an upper limit, but webservers may have one. In ASP.NET there is a default accept-limit of 4 MB, but you (the developer/webmaster) can change that to be higher or lower.
POST allows for an arbitrary length of data to be sent to a server, but there are limitations based on timeouts/bandwidth etc.
I think basically, it's safer to assume that it's not okay to send lots of data.
There is no limit according to the HTTP protocol itself, but implementations will have a practical upper limit. I have sent data exceeding 4 GB using POST to Apache, but some servers did have a limit of 4 GB at the time.
Different IIS web servers can process different amounts of data in the 'header', according to this (now deleted) article; http://classicasp.aspfaq.com/forms/what-is-the-limit-on-form/post-parameters.html;
Note that there is no limit on the number of FORM elements you can pass via POST, but only on the aggregate size of all name/value pairs. While GET is limited to as low as 1024 characters, POST data is limited to 2 MB on IIS 4.0, and 128 KB on IIS 5.0. Each name/value is limited to 1024 characters, as imposed by the SGML spec. Of course this does not apply to files uploaded using enctype='multipart/form-data' ... I have had no problems uploading files in the 90 - 100 MB range using IIS 5.0, aside from having to increase the server.scriptTimeout value as well as my patience!
Source: Stackoverflow.com