I'm running 4 #6 wires for a sub panel under ground about 90' the panel will be 60 amps i want to use pvc but need to know the right size to get to hold all this. There will be 2 90s and a pull box on each end.
1" PVC would work.
Just so you know, you can run a #10 ground for this. It does not need to be #6.
Also, why the pull boxes?
Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.
Answers based on the 2008 & 2011 NEC. If you're on the '14 already I feel sorry for you.