14 C.F.R. § 121.115
(a) Routes and route segments over Federal airways, foreign airways, or advisory routes have a width equal to the designated width of those airways or advisory routes. Whenever the Administrator finds it necessary to determine the width of other routes, he considers the following:
[Docket 6258, 29 FR 19195, Dec. 31, 1964, as amended by Amdt. 121-253, 61 FR 2610, Jan. 26, 1996]