The only information I could find claims that about 22% of reddit is NSFW. They calculated the percentage of NSFW subreddits with >100k subscribers. [1]
That's far from a perfect way to measure this, but it's around the statistic that 30% of the internet is porn. My intuition tells me Reddit probably reflects the internet as a whole pretty well.
Doesn't matter the percentage of subreddits (i.e. counting every qualifying subreddit equally), what is the percentage of eyeballs? And don't you think lots of people view porn subreddits without subscribing?
Well, just for the record, that doesn't invalidate what I said. I'm not concerned with what PERCENTAGE is porn. It still is the largest, most-easily-accessible, most searchable, free porn site. And also for the record, yes, I HATE that Reddit (and Twitter, et. al.) allow full-on NSFW content along with all the rest.
That's far from a perfect way to measure this, but it's around the statistic that 30% of the internet is porn. My intuition tells me Reddit probably reflects the internet as a whole pretty well.
[1] https://www.reddit.com/r/dataisbeautiful/comments/f94j0y/oc_...