From http://httpd.apache.org/docs/2.2/misc/perf-tuning.html

The single biggest hardware issue affecting webserver performance is RAM. A webserver should never ever have to swap, as swapping increases the latency of each request beyond a point that users consider "fast enough". This causes users to hit stop and reload, further increasing the load. You can, and should, control the MaxClients setting so that your server does not spawn so many children it starts swapping. This procedure for doing this is simple: determine the size of your average Apache process, by looking at your process list via a tool such as top, and divide this into your total available memory, leaving some room for other processes.

The main issue is that I can't understand how to know the size, because, well i have the size of httpd on no more of 3888

But, if we need to determine the number for MaxClients, and I have 4GB of RAM, so I get: 972, so I should use like 900 in the MaxClients?