my MacBook Pro had 16gb ram and it uses 8.9gb ram when its on idle is it normal

"Free RAM" as a useful metric in Macs disappeared with Mac OS 10.9 in Oct 2013. For the last seven years, the applicable metrics have been "Memory Pressure" and "Swap."

In this real world example, you can see the new system at work:

Although over 11GB of the 12 GB of RAM was "used," pressure is nil and "Swap" is zero. The computer was working perfectly.

Unused RAM is wasted RAM. Your MacOS manages RAM very well. RAM temporarily stores data in preparation for use so that computer response time will be faster. If nothing was in RAM then your computer would respond much more slowly.

kaidzohar wrote:

my MacBook Pro had 16gb ram and it uses 8.9gb ram when its on idle is it normal

Normal.

Are you having some issue?