What is the fill for 3/4 PVC conduit?

Three quarter inch Schedule 40 PVC gives you 0.203 square inches of usable area at the NEC's 40 percent fill, which works out to 15 number 12 THHN conductors or 9 number 10s.

Schedule 80's thicker wall shrinks that noticeably, to 12 number 12s. PVC always trails EMT at the same trade size because the plastic wall is fatter.

The 40 percent applies at three or more wires; one wire gets 53 percent and a pair gets 31.

Count every conductor including grounds for fill purposes, and then remember derating counts differently: more than three current-carrying wires and each one's ampacity drops, which usually binds before the pipe is physically full.

The PVC conduit wire count calculator has both schedules and every conductor size loaded.