In a standard AM signal, the frequency spectrum consists of the carrier frequency $f_c$ and two sidebands:

• Upper Sideband (USB): $f_c+f_m$
• Lower Sideband (LSB): $f_c-f_m$ where $f_m$ is the frequency of the modulating signal. The bandwidth ($BW$) is the difference between the highest and lowest frequencies: $BW=(f_c+f_m)-(f_c-f_m)=2f_m$. Thus, the bandwidth of an AM signal is twice the highest frequency present in the modulating signal.