Where do I see the number of my unique visitors in Google Analytics?

To determine the optimal pool size, we are guided by the unique visitors per month

I see the unique visitors/users on the start page.

Take the last complete month as the period. In case of fluctuations, compare the last 3 months to get an average value.

The unique visitors can now be found under users:

Based on this number, the pool size can now be determined to get the best tracking results:

How do I calculate the correct pool size for my website?