Signal-to-noise and distortion ratio (SINAD) is a measure of the quality of a signal from a communications device, often defined as

${\displaystyle \mathrm {SINAD} ={\frac {P_{\text{signal}}+P_{\text{noise}}+P_{\text{distortion}}}{P_{\text{noise}}+P_{\text{distortion}}}},}$

where ${\displaystyle P}$ is the average power of the signal, noise and distortion components. SINAD is usually expressed in dB and is quoted alongside the receiver RF sensitivity, to give a quantitative evaluation of the receiver sensitivity. Note that with this definition, unlike SNR, a SINAD reading can never be less than 1 (i.e. it is always positive when quoted in dB).

When calculating the distortion, it is common to exclude the DC components.

Due to widespread use, SINAD has collected several different definitions. SINAD is commonly defined as:

1. The ratio of (a) total received power, i.e., the signal to (b) the noise-plus-distortion power. This is modeled by the equation above.
2. The ratio of (a) the power of a test signal, i.e. a sine wave, to (b) the residual received power, i.e. noise-plus-distortion power. With this definition, it is possible to have a SINAD level less than one. This definition is used in the calculation of ENOB for DACs and ADCs.

Information on the relations between SINAD, ENOB, SNR, THD and SFDR can be found in.