I took a bottom up approach starting from No/ of Internet users in the world (3.5 billion)
We can assume that Youtube Penetration is 90% of internet-using population (3.2b)
In the Youtube Penetration there are majorly 2 classes - Creators(5%) and Viewers (95%)
Since we are focused on Creators, lets explore this category further.
Of the Creators we have 3 categories
1. Professionals (10%) - Who upload an average of 1 video per week (4 per month)
2. Hobbyists (40%) - Who upload an average of 1 video per month
3. Indvidual Accounts (50%)- Who upload an average of 1 video per year (1/12 per month
5% of creators give us 160m people
Videos by Professionals/ month - 160m*(0.10)*(4) = 64m
Videos by Hobbysit/ month - 160m*(0.40)*(1) = 64m
Videos by Individuals/month - 160m*(0.50)*(1/12) = 7m
Total videeos = 64+64+7 = 135m
Calculated this and it checks out with the sanity checks! Please let me know, if there's any improvement that can be done in this approach.