This paper presents an innovative solution for enhancing cyber-security in critical infrastructures. The proposed approach focuses on measuring cyber-security maturity and identifying key risk areas through the use of a formal intelligent metric system. The system aims to assist the cyber-security assessment process by comparing the level of maturity against good practices or national requirements of critical infrastructure entities. The knowledge base of the formal intelligent metric system contains five maturity levels, which cover both technological and human dimension criteria. The system is universal for the field of critical infrastructure and helps increase the level of cyber-security maturity while minimizing risks. The system can be used as a standalone solution or complement previously proposed decision support systems. Furthermore, it can be adapted to any type of critical infrastructure, depending on the context and requirements. This paper provides an overview and description of the formal intelligent metric system, discusses its potential use cases in the critical infrastructure domain, and highlights possible adaptations given the context of each entity.