I got the 1M estimate from here. 4.2M == 1M in astronomer math. > Let’s say we use an assumption for average addresses per person to be 10 — which is just a rough guess — then the ceiling of bitcoin users who have their own addresses is around 4.2 million.

Bitcoin Magazine

You’re Still Early: An Objective Look At Bitcoin Adoption

How many bitcoin users are there? How should we define a bitcoin user? An analysis for categorizing and tracking user growth compared to other esti...