Within a 1/2 in PVC conduit body there is 4 cu in of space. When applying the wire volume rules to conductors entering this body it seems that this size body is not very useful. For example, if I were to use #12 wire (volume = 2.25) I would only be allowed to have 1 conductor entering the body, because it's only 4 cu in.

Have I gone wrong in this calculation?

Mike,
If you are not splicing in the conduit body then the maximum number of conductors is maximum number permitted by table 1 or chapter 9 for the conduit or tubing to which it is attached...
If you are splicing then use 314.16(C)(2).

Mike,
If you are not splicing in the conduit body then the maximum number of conductors is maximum number permitted by table 1 or chapter 9 for the conduit or tubing to which it is attached...
If you are splicing then use 314.16(C)(2).

I will not be splicing. Thank you very much. That makes sense. It's just the answer I wanted to hear.

I'll be using #12 THHN in 1/2" sch 40 PVC and it looks like 8 conductors are permitted. More than I want.

I'm grateful that you're here for us.
Michael

8 are max fill, but more than 5 and you have to derate them

Just sayin'

Shunt...
More than 3 and you have to derate..

More specifically... more than 3 "current carrying conductors"...

In this case with #12 AWG THHN 90C copper, (most likely),
Eight #12 derate to 70% which would be 21 amps... 12 AWG is required
To be protected by a 20 ampere overcurrent so here the derating is somewhat
Of non-issue...