This research compares Ordinary Portland Cement (OPC) and Limestone Calcined Clay Cement (LC3) to study their heat of hydration and strength characteristics by varying aggregate sizes. Four samples of each cement type were tested, with different coarse aggregate sizes used in each specimen. Among the four specimens, three had simple aggregate sizes of 1/2 in., 3/8 in., and 3/4 in., while the remaining one was consisted of combination with 30% 3/8 in. and 70% 1/2 in. The heat of hydration was measured using an isothermal calorimeter to evaluate the impact of aggregate size and grading differences. Cylindrical specimens, as per ASTM C39, were also prepared for each cement type using the same mix design to assess compressive strength. These cylinder samples were tested to validate the heat of hydration curves. The study provides insights into how aggregate size and grading influence the heat of hydration and compressive strength for OPC and LC3 cements. By comparing the two cement types under different conditions, the research aims to establish a clearer understanding of the relationship between heat of hydration and compressive strength, offering valuable information for practical applications in construction.