This is so simple
1. Go to your Google + account (https://plus.google.com/).
2. Click on the Profile icon on the Left.
3. If you look at the URL in the address bar, it should look something like this:
https://plus.google.com/104653270154306099169/posts
4. The long numerical string in the URL is your Google+ ID. Here is CoderzHeaven’s from the URL above:
104653270154306099169/