Voltage really depends on so many factors. I will just name a few.
-Distance from step down transformer (the thing that converts the high voltage from power lines to 120/208 or 120/240 that feeds your house).
-How many times that feed is split for all dwellings on that grid.
-How well the electrician who wired your house designed the layout for balanced neutrals on all of the circuits.
-How many unbalanced loads, overloaded circuits, and even how many bends there are in the wire from the circuit breaker to the outlet.
There really are many transients that affect voltage potential but luckly most of our devices in this country operate within 108vac to 127vac. So minor variances as well as surges, spikes, and dips don't affect the "normal" operation on a day to day base. Allot of equipment lifespan could be extended if we could actually narrow that window down to a regulated voltage. In an ideal situation, you would balance the positive 60volt wave form on the hot side and the negative 60volt wave form on the neutral side, you would get a perfect wave form of 120 volts between hot and neutral.