Designed for learners in metallurgy, materials science, and mechanical engineering, this course provides an in-depth exploration of grain size measurement techniques and strengthening mechanisms in steels. Through five structured modules, learners progress from foundational concepts of grain boundary analysis and quantitative metallography to advanced mechanical property predictions using grain-dependent models. The course emphasizes both the Mean Linear Intercept (MLI) and ASTM methods, and introduces the Hall-Petch theory to explain the influence of grain size on yield strength, toughness, and Ultimate Tensile Strength (UTS). Real-world studies and equations, such as those from Mintz, Baird & Cochrane, support analytical skills development and the application of metallurgical theory. Ideal for engineers and scientists aiming to quantify microstructural features and link them to mechanical performance in structural metals.