Conduit fill for LV and fiber cables should always be obtained from the manufacturer of the cable. Of importance here is pulling tension, nothing else. Putting too much stress on a cable while pulling it will damage it.
It's not simply a matter of applying NEC tables, and other rules, to datacom wire. The NEC was never intended for such applications.
For example, typical Cat 5 specs limit your pulling force to 25 lbs ... total. It matters not how many cables are being pulled, 25 lbs is the limit.
Another insight may be obtained from phone co. specs for their lines. They'll want a 4" pipe, with a maximum of 2-90's in bends, for a single 25 pair line. (A 25 pair line is something like 5/8" OD).
Finally, I recently pulled a single 3-pair cat 3 cable through a 1/2" PVC pipe to a detached garage. While the pipe seemed plenty large, the pull was harder than I expected. It's the last time I'll make that mistake .... I think I'll START with 1" for any but the shortest cable drops.
The Nec your right is not Made for data as far as wire fill ect but its sure better then the way most do it. That is hold a bunch of wires in there hand and see how many fit in the pipe, forgetting they'll be pulling around bends and 90's. Been working for me for years pullings great. as far as Phone company a 25 pair in a 4 inch is a joke .That 4 inch at 51 percent fill would fit easly in a 1 1/4 inch . Thats just there way if we all went by fillpercentage instead of Geeee What well fit I;ll try this.
Then go to Chaper 9 table 4 Percentage fill charts...as far as Phone company a 25 pair in a 4 inch is a joke.
If you want to do another trades job you have to stop thinking like an electrician and learn how that work is done. The question of LV conduit fill comes up frequently and the replys are always along the lines of "think of a THHN size that is similar and go to chapter 9 of the NEC". I don't know how many times we have said that this is wrong. You may get your cables pulled and they may even work but most likely they are no longer in spec.
I've NEVER EVER seen Data people with a Stress Gage on there wire pulls , Also they pull thru LB;s which does not meet most required pulling radias , Also most hire Kids to pull and install there wiring with no traning at all. As well as Proper Supports Forgets it they usually tie wrap to anything they can. Most Electricans install Data Cables far more correctly then the data people I;ve worked around and with. By the way do you use a Stress gage on yer pulls, and watch radias on pulls . :))) Just telling it the way it is in the real world . Been there done that
Believe me, you should have no trouble estimating pulling tension once you have been doing it. It's just like estimating how much something weighs. Problem is most installers, especially electricians think they are pulling THHN and yank the hell out of it because they don't know any better. That includes untrained data installers.