The relevance of the study of the quantitative dimension of genres, in particular genres of small format and short implementations of genres in general, has increased due to the need to “compress” information of various types in modern communications, insufficient knowledge of the patterns of functioning of short and abbreviated texts/discourses, attention to the quantitative aspects of speech in terms of their value. The problematic situation is defined by the author as a contradiction between the ascertainment of the prototypical nature of texts of small volume, rather complete descriptions of a number of small-format genres, on the one hand, and the lack of clarification of the factors that allow or do not allow the genre to function in a short (short, incomplete, abbreviated) mode. The purpose of the study is to identify and describe the circumstances that determine the external differentiation and internal variability of genres based on the quantitative characteristics of “brief” and “short”. It is a corpus research, the data about genres was formed on the corpus basis, the names of which formed the right contexts of the adjectives “brief” and “short” in the main body of the Russian National Corpus. It has been established that as “brief” are defined the realizations of genres that involve a written form, expansion, a rational strategy of text generation, standard content. “Short” versions are attributed to oral genres in which the subject of speech is free to choose the strategy and semantic content of the text. Brief forms can form institutionally fixed variants of genres, independent genres and represent individual realizations of the genre. The attitude of speech subjects to the choice of a short form depends on many pragmatic factors, it is rather approved than condemned.