What is the size limit of an HTTP POST request?

The URL portion of a request (GET and POST) can be limited by both the browser and the server - generally the safe size is 2KB as there are almost no browsers or servers that use a smaller limit.

The body of a request (POST) is normally¹ limited by the server on a byte size basis in order to prevent a type of DoS attack (note that this means character escaping can increase the byte size of the body). The most common server setting is 10MB, though all popular servers allow this to be increased or decreased via a setting file or panel.

¹ Some exceptions exist with older cell phone or other small device browsers - in those cases it is more a function of heap space reserved for this purpose on the device then anything else.

Also, in PHP.INI file there is a setting:

max_input_vars 

which in my version of PHP: 5.4.16 defaults to 1000.

From the manual: "How many input variables may be accepted (limit is applied to $_GET, $_POST and $_COOKIE superglobal separately)"

Ref.: http://www.php.net/manual/en/info.configuration.php#ini.max-input-vars

You can post large amount of data by setting php.ini variable: max_input_vars Default size of this variable is 1000 but if you want to sent large amount of data you have to increase the size accordingly. If you can't set the size from ini_set you have to do it through htaccess or by doing changes into php.ini file directly.

max_input_vars 2500 memory_limit 256M 

As David pointed out, I would go with KB in most cases.

php_value post_max_size 2K 

Note: my form is simple, just a few text boxes, not long text.

(PHP shorthand for KB is K, as outlined here.)

By default, the post request has maximum size of 8mb. But you can modify it according to your requirements. The modification can be done by opening php.ini file (php configuration setting).

Find

post_max_size=8M //for me, that was on line:771 

replace 8 according to your requirements.

One of the best solutions for this, you do not use multiple or more than 1,000 input fields. You can concatenate multiple inputs with any special character, for ex. @.

See this:

<input type='text' name='hs1' id='hs1'> <input type='text' name='hs2' id='hs2'> <input type='text' name='hs3' id='hs3'> <input type='text' name='hs4' id='hs4'> <input type='text' name='hs5' id='hs5'> <input type='hidden' name='hd' id='hd'> 

Using any script (JavaScript or JScript),

document.getElementById("hd").value = document.getElementById("hs1").value+"@"+document.getElementById("hs2").value+"@"+document.getElementById("hs3").value+"@"+document.getElementById("hs4").value+"@"+document.getElementById("hs5").value 

With this, you will bypass the max_input_vars issue. If you increase max_input_vars in the php.ini file, that is harmful to the server because it uses more server cache memory, and this can sometimes crash the server.

It is up to the http server to decide if there is a limit. The product I work on allows the admin to configure the limit.

For developers who cannot change php configuration because of the webhosting. (My settings 256MB max size, 1000 max variables)

I got the same issue that just 2 out of 5 big data objects (associative arrays) with substructures were received on the server side.

I find out that the whole substructure is being "flattened" in the post request. So, one object becomes a hundreds of literal variables. At the end, instead of 5 Object variables it is in reality sending dozens of hundreds elementar variables.

Solution in this case is to serialize each of the substructures into String. Then it is received on the server as 5 String variables. Example: {variable1:JSON.stringify(myDataObject1),variable2:JSON.stringify(myDataObject2)...}