I'm running a 60 amp circuit to provide power to my garage. It is about 70 ft in length, so I think I need to go with 4AWG to counter any resistance loss. I'll be pulling 4 wires (R,B,W,G) thru Schedule 80 PVC. According to Annex C, it looks like I need a minimum of 1 1/4 conduit, but I just wanted to confirm.
1" would be enough if it was Sch 40 pipe, presuming you're pulling 4 wires through it.
If you must use sch 80, you'll need to go with 1-1/4" pipe, which is technically bigger than required, but there's no intermediate size.
Upsizing makes your life easier
Since I doubt you have a truck loaded with nothing but pulling tools, you're better off upsizing the conduit to make your pull easier. Get some 2" or even 3" schedule 80 -- you'll be quite happy you did! (It also means you'll have room to put fatter wires down the pipe later if you want MOAR POWAH in the garage for some reason or another.)