Deeper for under driveways or roadways.
The general rule for buried PVC conduit (RNMC) is 18". If this is a single 120v
> 15a or 20a circuit, GFCI protected at the house end it can be 12", even if you
> used UF cable.
> Local frost heaving problems may make this moot, requiring that you get below
> the frost line but I don't know much about that (Florida boy).
> You are on the edge of worrying about voltage drop at 120'. I would say that if
> you are planning to run 70% or so of the ampacity of the wires you should bump
> it up a size. You should really do voltage calcs based on expected load. Then
> you can get real numbers. If this is just a convenience outlet for hand tools
> and a light in the shed you would be fine with 12ga. on a 20a.