In the present thesis different methods to determine the degree of inclusion content of high quality steels were compared. Using 2D and 3D methods. Methods such as light- and scanning electron microscopy assess an area of non-metallic inclusions on a polished surface. Fatigue tests at the range of gigacycle (GCF), computed tomography (CT), extraction of the steel matrix and the optical emission spectroscopy with pulse discrimination analysis (OES-PDA), and these methods investigate a volume of the sample. The experiments were performed on various tool steels, creep-resistant steel and hardenable martensitic stainless steel supplied by the steel industry. The high quality steels were produced by different production routes such as electric arc furnace (EAF) and subsequent secondary metallurgy (conventional production), as well as by EAF in combination with pressure electro slag (PESR) and EAF with vacuum arc (VAR) remelted materials. The aim of this study is to correlate the degree of inclusion content to results of 2D and 3D methods with each other as well as the conversion of 2D to 3D results using stereographic relationships followed by a comparison of all methods.