`curl https://api.github.com/users/YOUR_USER_HERE` then look for the id in the payload. "id": 2851

Or look at the html source of your avatar, https://avatars.githubusercontent.com/u/2851?v=4

Huh, I'm in the late 150000's. I was genuinely expecting it to be in the millions.

go to a profile and open image in new tab, the URL is /u/# (im # ~4 million!)

It shows up in API responses when you look up your own user.