One option is to use smem
as free does not offer this functionality.
$ sudo smem -u -k -t
User Count Swap USS PSS RSS
daemon 1 0 196.0K 197.0K 360.0K
rtkit 1 0 304.0K 317.0K 1.4M
[...]
root 44 0 164.3M 197.7M 284.4M
gert 88 0 1.7G 1.8G 3.2G
---------------------------------------------------
159 0 1.9G 2.1G 3.6G
For explanation on what USS and PSS means, here's an excerpt from the manpage of smem.
[...] Unshared memory is reported as the USS (Unique Set
Size). Shared memory is divided evenly among the processes shar‐
ing that memory. The unshared memory (USS) plus a process's pro‐
portion of shared memory is reported as the PSS (Proportional Set
Size). The USS and PSS only include physical memory usage. They
do not include memory that has been swapped out to disk.
I suspect RSS is the Residential memory usage also referred to as RES in other utilities. For more information on expression of memory usage see this Q&A on Superuser.com: What I should know about memory management?