The size distribution of bubbles is a key factor in characterizing the sonochemical reaction field. The assessment of bubble population within cavitation fields induced by sonication has led to the development of various experimental and theoretical techniques. While experimental methods provide valuable baseline data for comparison, their limited number and the complexity of cavitation fields restrict their ability to fully characterize bubble dynamics. In contrast, theoretical calculations based on cavitation models for reactive bubbles have made significant advancements in the last decade, enabling bubble size analysis over a wide range of operational conditions. This chapter offers an in-depth exploration of computational methodologies and results rooted in reactive bubble sonochemistry to determine bubble distribution within acoustic fields. The chapter begins by reviewing key experimental findings to provide context and establish a foundation for the subsequent theoretical analysis. Ultimately, the chapter presents a wealth of data and insights on active bubble size distributions, aiding in the design of sonochemical reactors for different homogenous sonochemical processes.