The notion «Dimension» is one of system-forming lines of Mathematic course at primary school. In the article it is mentioned, that the idea and notion formation of dimensions and their calculating practically goes beyond Math course and has general cultural value, because imagination and notion data are widely used in studying other subjects, in familiarization the child with surrounding world and further in the practice of the adult. This fact is a reason of polysemy of this notion, that is a turn of different ways of its notion and makes difficulties both in the awareness of the notion dimension and in the methods of its teaching. The result of such variegated is the mixing of notions, that contradict one another and so break the correctness of terminology, that corresponds the real content of the theory of dimension notion, in fact, that is the actuality of the work. In the article, on the basis of the world level scientists’ researches, the notion of dimension is studied in two meanings – general scientific and substantive. It is mentioned, that in general scientific sense «dimension» is the object property to be measured, namely compared with another object of the same plurality. In this sense, the expression «dimension of size» is correct. In substantive meaning «dimension» is the characteristics of the object’s property, that is signified in units (measure). In this sense, the notion dimension means giving quantitative characteristics of the measured object. That’s why the expression «calculating of dimension» is correct here. In the article the essence of scalar quantities is described, the description of measuring procedure is done and on its basis the content of the dimension definition as the unit of object is defined. According to this, in the article the terminology accordingly the objects’ measuring and calculating their dimensions is corrected, the definitions of the dimensions, that are studied at primary school, namely length, square, size, mass, time are given in the correct form. As a result, a unique opportunity of the correct attitude toward the terminology both in formulation Mathematic notions, relations and in usage in practice are marked. The purpose of the work is to reveal an informative component of the methodology of studying values in a new Ukrainian school. The methodology includes the research of the scientists who point out the two meanings of the concept «value» – the general scientific and subject one. Scientific novelty – the correct formulations of definitions of quantities studied in the new Ukrainian school are given. Conclusions – the importance of correct attitude to the linguistic aspects of the presentation of educational material both while formulating mathematical concepts and relations, and while using them in practical activities.