size of thread's stack


I have set thread’s stack to 8KB (via call to pthread_attr_setstacksize()),
and then created thread by calling pthread_create(). When I run

pidin mem | grep

it shows that thread’s stack size is “4096(12K)”. Could somebody please
clarify what 4096 stands for, what is the actual size of thread’s stack,
and a possible reason why it’s different from 8 KB.

Thanks in advance,