Concrete is the most complex artificial material and most commonly used in structural engineering. There are many advantages over other constructive materials. It is characterized by its high compressive strength, which is the basic measure of its quality. The strength of concrete is defined as the concrete class. It is determined as the mean value of the concrete compressive strength, measured on 28 days old concrete cubes, with the dimension of the cube being 20cm. One of the main requirements of concrete is the verification of conformity carried out on the results of the factory production control and the test results of compressive strength of concrete tested on random samples. Procedures for conformity assessment and for issuing conformity documents are carried out according to Construction Products Act (OG 76/13) and Ordinance on conformity assessment, documents of conformity and the marking of construction products (OG 103/08). Conformity or non-conformity is determined according to conformity criteria, which are different depending on whether concrete control is being carried out in the production or on the construction site. In this paper, the identity of the compressive strength of concrete is investigated by applying the norm HRN EN 206-1: 2006 Concrete - Part 1: Specification, performance, production and conformity, to check whether the compressive strength of concrete is in accordance with the characteristic strength. The results are presented as a normal (Gauss) distribution.