How many 14/2 romex cables can I put in a 1/2 pvc conduit?
Use individual THWNs here instead, or else prepare to face the full wrath of the fill rules (and the electrician that comes over to rescue your pull job!)

A 1/2" schedule 80 PVC conduit has 56mm2 of usable fill for individual wires, or 75mm2 of usable fill for a single wire or cable.  A 14AWG THWN takes up about 6.3mm2 of fill; however, a multiconductor cable's fill is computed as if it were a round wire with a diameter equal to the major diameter (long dimension) of the cable (Note 9 from chapter 9 of the NEC):


  (9) A multiconductor cable, optical fiber cable, or flexible
  cord of two or more conductors shall be treated as a
  single conductor for calculating percentage conduit fill
  area. For cables that have elliptical cross sections, the
  cross-sectional area calculation shall be based on using
  the major diameter of the ellipse as a circle diameter.


As a result of this, given that a 14/2 UF cable has dimensions of 0.185" by 0.385", as per Encore Wire's specsheet, or 4.7mm by 9.8mm in handier units, we then get an effective fill area for a single 14/2 UF cable of just over 75mm2!

Given that a single 14AWG bare copper conductor for the EGC counts for 2.1mm2 of fill, you can get 4 hots and 4 neutrals (i.e. 4 circuits) + 1 EGC (which all 4 circuits can share) into your conduit without busting the 56mm2 fill limit and allowing the conductors to carry their full permitted 15A still due to the way the derate rules work.  Compare that to the 75mm2 UF cable not quite fitting down the conduit by Code, making you emit profanity all the way through the pull, while only providing a single circuit to wherever this is going.

(Of course, this conduit will let you run a bigger feeder there if you want multiple circuits at the destination, too -- you could get 3 10AWG THWNs + a bare 10AWG ground down there and power your 4 15A circuits from a subpanel that way, instead of stuffing more 14AWG wires down the conduit.)