How can I determine how much total RAM my device actually has?
I know this is an old questions but it comes up first in Google so I thought I would put a simple answer.

Depending on the version of Android:


Settings > Applications > Running services
or Settings > Apps > Running services
or Settings > More > Application Manager > Running (at the top)
or Settings > System > Developer Options > Running services


At the bottom you will see RAM, used and free.  Add both number together to get total usable RAM for the device. Note that this might be less than the RAM advertised for the phone model, as the system may reserve some of the RAM for itself as explained in other answers.

Cheers