How many wires can I fit in 1" schedule 40 PVC conduit?
TL;DR No.
Chart in answer at: How do I determine the fill rating of a conduit?

1&quot; Schedule 40 @ 40% = 0.333 in2
8 AWG = 0.0366 in2 x 4 = 0.1464 in2
6 AWG = 0.0507 in2 x 4 = 0.2028 in2
0.1464 + 0.2028 = 0.3492 &gt; 0.333

There may be additional issues of how many circuits and/or types of circuits in the same conduit. But 0.3492 &gt; 0.333 so it doesn't matter.