The following table lists the various classes of FM stations, the reference facilities for each station class, and the protected and city grade contours for each station class. A contour may be visualized by imagining a rough circle surrounding a transmitter site at some distance, where the circle represents a certain field strength value, with greater radio field strengths inside, and lesser radio field strengths outside. The distances to the contours herein were derived using the maximum effective radiated power (ERP) and antenna height above average terrain (HAAT) combination permitted for each station class (see Section 73.211), and assumes uniform (flat) terrain in all directions. In practice, the distances to a specified contour for a given FM station in a given direction will vary from the listed value depending on the effects of terrain in that direction.

The listed values are for commercial FM stations. This data also holds true for noncommercial educational stations, except that the 70 dBu city grade requirement of 47 CFR Section 73.315(a) does not apply to noncommercial educational stations in the portion of the FM band reserved for noncommercial educational use (88.1 to 91.9 MHz). Please note, however, that the 60 dBu contour must encompass 50% portion of the community of license. In addition, please note that the distances to reserved band noncommercial educational stations' protected contours for Class B and Class B1 stations are the same as the distances listed for Class C2 and Class C3 stations, respectively, since the protected contour for all reserved band stations is 60 dBu ( 1.0 mV/m ).

For different combinations of ERP and HAAT, you may determine the applicable FM station class by using our FM propagation curves calculations program and comparing the result with the table below. Be sure to use the 60 dBu F(50,50) contour, since it is on the basis of that contour (not the 70 or 54 or 57 dBu contour) that equivalence between facilities is determined.

In addition, if you know the station class and the antenna height above average terrain (HAAT), you may use our FMpower program to calculate the effective radiated power (ERP) needed to achieve maximum coverage for the selected station class. This program will also advise whether the station class is valid in the selected state.

[ For FM minimum separation requirements, especially for commercial FM stations, please see our document FM Radio Station Spacing Standards. ]

Notes: Class B and B1 stations are authorized only in Zones I and I-A, which include the following states and areas: CA (south of 40° latitude), CT, DC, DE, IL, IN, MA, MD, coastal ME, MI (south of 43.5° latitude), NJ, NH (south of 43.5° latitude), NY (south of 43.5° latitude), OH, PA, PR, RI, northern & eastern VA, VI, VT (south of 43.5° latitude), southeastern WI, WV. Class C, C0, C1, C2, and C3 stations are not authorized in Zones I or I-A, but may be authorized elsewhere. See Section 73.205 for the exact zone boundaries. You may also use FMpower to determine whether a particular class is valid in a given state.