Generally more than just the motor size is used to specify the delineation between moped and motorcycle. Usually a bike that is considered a moped or scooter and thereby not requiring a motorcycle permit is usually restricted by wheel size (having one or more wheels that is 10"or more) and by brake horsepower(no more that 2.5 bhp).You can look up the moped laws for your state here:http://moped2.org/mstates.htm