What is the size limit of an HTTP POST request?

Sorry if this is duplicate,I would think it would be but couldn't find anything. I have a flex application that I am posting data back to a PHP/MySQL server via Internet Explorer. I haven't run into any problems yet, but knowing this ahead of time might save me a bunch of frustration and work. Is there a size limit to posting data via HTTP? - This article says "no": http://www.netlobo.com/ie_form_submit.html - This discussion says "yes": http://bytes.com/topic/php/answers/538226-what-maximum-limit-using-post-method And it all goes back and forth what I'm able to find online. So **please** limit answers to personally tested/verified numbers. I am wanting to post back an XML string that can be quite large (say up to 5mb). If it makes any difference: browser will always be Internet Explorer (our product requires it), POST is coming from an `HTTPService` in Flex, web server is PHP, database is MySQL.