Free RAM is a pointless thing to ask.
Android works exactly like desktop Linux in this regard, it stuff the system files (OS) into the RAM, then it decides how much to leave free, then it calculates how much spare it has, then it stuffs that with the things that are used most often.

So if you have 1GB RAM, and the OS consumes about 200MB, and you've elected to leave 100MBs free. Android will calculate that it has 700MB of free RAM. Then it will look at all your Apps. Lets say the total of your Apps is 1.5GB, well Android will take the first 700MB of Apps... ones that are used most often.

You'll have roughly 100MB of free RAM... but when you are doing normal things (OS-bound) things will be snappy. When you use your apps, most often, it will pop right open because its right there ready to be accessed inside the RAM. When you click on a function or App that is seldom used... the OS will have to pull that out from your SSD/NAND or the microSD-slot (basically wherever it resides). And there will be slow delay as the OS kills off certain things in the RAM and attemots to load the function/app into the RAM.

Its a basic concept, and it works wonderfully.