In telecommunication, a Carson bandwidth rule is a rule defining the approximate bandwidth requirements of communications system components for a carrier signal that is frequency modulated by a continuous or broad spectrum of frequencies rather than a single frequency.

The Carson bandwidth rule is expressed by the relation CBR = 2(Δf + f _m) where CBR is the bandwidth requirement, Δf is the carrier peak deviation frequency, and f _m is the highest modulating frequency.

The Carson bandwidth rule is often applied to transmitters, antennas, optical sources, receivers, photodetectors, and other communications system components.