How many #12 wires can you put in a 1/2 conduit?

Nine number 12 THHN conductors fit in half inch EMT under the NEC's 40 percent fill limit. That is the standard answer for the standard case.

Change any variable and the count moves. Half inch Schedule 40 PVC takes fewer because its inner diameter is smaller. Thicker insulations like THW drop the count further.

A 12-2 Romex cable is a different story entirely: its flat profile counts at its widest dimension, and realistically one cable is what a half inch pipe accepts.

Remember the derating trap: more than three current-carrying conductors in one conduit means reducing each wire's ampacity, so nine wires that fit may not all be usable at 20 amps.

The conduit fill calculator counts fill and flags the derating threshold in the same result.