This research provides a numerical investigation into the thermal and hydraulic performance of a pin-fin heat sink, considering the effects of fin radius, fin length, and the arrangement of the arrays. A 3D computational model was developed and solved in ANSYS Icepak for conjugate heat transfer and fluid flow under forced convection. The fin length was changed from 1 cm to 8 cm, and the fin radius from 1 mm to 6 mm. Inline and staggered configurations were investigated for the two types of arrangements to assess their effect on performance. The findings underscore an important trade-off between thermal resistance and pressure drop. As anticipated, the staggered configuration provided a consistent increase in the heat transfer coefficient because of better flow mixing and disruption of the thermal boundary layers. This improvement, however, came with a significantly higher pressure drop. From the analysis, it was evident that the best configuration is strongly influenced by the length of the fins. With shorter fins of 1-3 cm, the staggered array decreased thermal resistance far better than the in-line array. With longer fins of 6-8 cm, the in-line configuration frequently provided better overall performance because the mass flow rate was higher due to less pressure drop than the long, staggered path. In addition, the radius of the fin exhibited a nonlinear relationship with regard to performance. Increasing the radius provided a greater area for heat dissipation, but it also increased obstruction to the flow. For every specific length and arrangement combination, a thermal performance maximizing radius existed. This work gives important design rules for the thermal optimization of the heat sink geometry and emphasizes the importance of the staggered array, for short fin lengths, while revealing the in-line configuration advantage for long fin lengths when minimizing pressure drop becomes the main concern.