<p>This study employed both numerical and experimental methods to evaluate heat transfer in Newtonian fluid flow through helical coils with varying cross-sectional geometries, while maintaining identical flow areas. To the authors’ knowledge, no prior experimental-numerical study has systematically examined this topic. Three pairs of helical coils with circular, square, and rectangular cross sections, all possessing identical flow areas, are utilised for the experimental studies. A custom-built isothermal steady-state experimental setup is used for evaluating heat transfer through water in laminar to turbulent flow regimes. Heat transfer parameters based on local heat transfer equilibrium are estimated using experimental data. The average heat transfer coefficients are found to be higher for the coils with rectangular cross-sections and lower for the circular cross-sections. For the first time, seven novel correlations, including a generalised one, are developed, linking the Nusselt numbers of helical coils with their respective non-dimensional M numbers, for industrial design applications.</p>