We are adding a bathroom and need to know how far from the wall side and back the drain/sewer pipe need to be. Don't want to cut the hole in the floor and have the flange be to close to set toilet. I have heard different numbers. IE 13" and 15-16". We are in need of this information asap. Thanks in advance...

The standard distance is 12" to center from a unfinished wall or 11 1/2" from a finished wall.
Regards, Tom

Tom is right on the back wall, 12".: Side is, in most locations, 15" from center of flange to sidewall .