It changes why?
How many masters are there?

It will be tough to get an exact figure since record keeping isn`t up to snuff.
So I would think if someone does find an answer it might be a reasonable estimate but that is all.

I've come across some statistics like these over time and the #'s you're seeking are pretty impressively low. It makes the chess world seem much smaller than it actually is when you see just how few reach that level.

You guys got me curious so I slogged through a google search without, surprise surprise, finding current statistics. Best I could do was from 2010 but the following does have stats for most titles back then. Add maybe 10 to 20% for current numbers?
http://en.wikipedia.org/wiki/FIDE_titles
There are 200+ nations. Being a National Master of different nations may represent quite different levels.
Who is the lowest rated national chess champion, which nation?

As of writing this comment, 19518. calculated by the number of titled players in this link: https://ratings.fide.com/topfed.phtml

As of writing this comment, 19518. calculated by the number of titles players in this link: https://ratings.fide.com/topfed.phtml
That wouldn't account for NMs in countries that have them who don't also have a FIDE title

As of writing this comment, 19518. calculated by the number of titles players in this link: https://ratings.fide.com/topfed.phtml
That wouldn't account for NMs in countries that have them who don't also have a FIDE title
Yep, NMs are not issued by Fide, so I'd assume this link doesn't include NMs - though not sure. they are issued by the country. So, in Fide there are 19518 titled players.
I am having trouble finding these stats. How many Experts, National Masters, Fide Masters, International Masters are there? I found Grandmasters on a previous thread.