A comprehensive comparison of fluid flow and heat transfer characteristics inside a square enclosure with water or liquid gallium as fluids under natural convection has been studied numerically in the laminar flow regime. The left and right walls of the square cavity are treated as hot and cold isothermal walls, respectively, while the other walls are kept adiabatic. A 2D problem is considered, and the buoyancy term in the momentum equation is represented by the Boussinesq approximation. The governing equations are solved using finite difference methods. The convective terms are evaluated by using sixth-order compact schemes. Results are shown in the form of isotherms, streamlines, temperature profiles, average Nusselt number, average heat transfer coefficient values, and average skin friction values for various Grashof numbers (Gr) ranging from 103 to 106. The present solver is validated against numerical and experimental work published in the literature. From the study, it is observed that the flow and heat transfer characteristics of conventional fluids like water differ significantly from low Prandtl number fluids like liquid gallium. Results show that the diffusion mechanism is dominant compared to convection in liquid gallium as a fluid for Gr ≤ 104, but the convection phenomenon is dominant in water as a fluid for all Grashof numbers. The comparison shows that at a Grashof number of 103 liquid gallium has 25.61 times greater heat transfer than water. Finally, a correlation for the average Nusselt number is developed with liquid gallium as fluid for a Grashof number ranging from 103 to 106 © 2023 by Begell House, Inc.