Does anyone have a figure for this number? If not, and you're curious, for a few rifts, you could keep track of your profile elite kills, as well as your number of rifts, and post that information and I can aggregate it and return with the results.
Very very very roughly: 500 monsters per rift until you spawn the guardian. (Just one source, I remember there were much more months ago but didn't bookmark them.) However, it can sometimes be 250 or 750, if you Google for other people who have tried to track this.
Now, there are rifts with almost only elites (especially quite often on cemetery) or quite few elites. And there's also a huge variance in how many you have to kill to spawn the guardian; sometimes you go on for much longer *after* the guardian is dead, sometimes you need to kill almost every mob to spawn the guardian. Let's take the average from the source I linked above, and there should be about 56 elites in a rift until getting to 100%. However, notice the outliers (ranging from 9 to 0 (!)). And 10 rifts is an insanely small sample.
This variance is being reduced significantly in Greater Rifts on PTR; although I haven't spent too much time on PTR and it's not perfectly even, I felt that they've done a good job to minimize those crazy outliers. What makes rifts feel different in difficulty though is that some monsters (act 5 mobs) are just much harder. Oh, and elite kills seem to count much more on PTR.
TL;DR: Probably about 50 elites per rift (until spawning the guardian), but with a huge variance of plus/minus 25 or so.
If you want more reliable data just track your kill numbers and run many many rifts (100+) to get an average. I somehow am not too keen on getting community data to aggregate this, to be honest. You'll always have people who skew your data because they feel this is an e-peen test about "who gets the rift with most elites" and stuff, reporting wrong data.
Very very very roughly: 500 monsters per rift until you spawn the guardian. (Just one source, I remember there were much more months ago but didn't bookmark them.) However, it can sometimes be 250 or 750, if you Google for other people who have tried to track this.
Now, there are rifts with almost only elites (especially quite often on cemetery) or quite few elites. And there's also a huge variance in how many you have to kill to spawn the guardian; sometimes you go on for much longer *after* the guardian is dead, sometimes you need to kill almost every mob to spawn the guardian. Let's take the average from the source I linked above, and there should be about 56 elites in a rift until getting to 100%. However, notice the outliers (ranging from 9 to 0 (!)). And 10 rifts is an insanely small sample.
This variance is being reduced significantly in Greater Rifts on PTR; although I haven't spent too much time on PTR and it's not perfectly even, I felt that they've done a good job to minimize those crazy outliers. What makes rifts feel different in difficulty though is that some monsters (act 5 mobs) are just much harder. Oh, and elite kills seem to count much more on PTR.
TL;DR: Probably about 50 elites per rift (until spawning the guardian), but with a huge variance of plus/minus 25 or so.
If you want more reliable data just track your kill numbers and run many many rifts (100+) to get an average. I somehow am not too keen on getting community data to aggregate this, to be honest. You'll always have people who skew your data because they feel this is an e-peen test about "who gets the rift with most elites" and stuff, reporting wrong data.