This document specifies requirements for ultrasonic attenuation spectroscopy methods for determining the size distributions of a particulate phase dispersed in a liquid at dilute concentrations, where the ultrasonic attenuation spectrum is a linear function of the particle volume fraction. In this regime particle-particle interactions are negligible. Colloids, dilute dispersions, and emulsions are within the scope of this document. The typical particle size for such analysis ranges from 10 nm to 3 mm, although particles outside this range have also been successfully measured. For solid particles in suspension, size measurements can be made at concentrations typically ranging from 0,1 % by volume up to 5 % by volume, depending on the density contrast between the solid and liquid phases, the particle size, and the frequency range,. For emulsions, measurements can be made at much higher concentrations. These ultrasonic methods can be used to monitor dynamic changes in the size distribution.