I used to have all types of charts for that kind of thing but it all went away when I hung it up..
The clients sometimes have their minimums that can be found in the General Electrical Specs,,,,,,You will find any hard fast rules. The most used controlling factor would be the turn radius of fittings plus some wrench clearance. We did use a mininmum of 4" center to center for 3/4"conduit and worked up from there for larger sizes.
dick
