Inherent reliability and enhanced passive safety has made natural circulation loop a very popular mode of heat transport, particularly in the fields of nuclear reactor heat removal and emergency core cooling. Despite a wide range of applications and a large volume of available research studies, the disparity in modeling approaches for single-phase NCLs is very much apparent. Varieties of standards have been adopted and diversified definitions of characterizing parameters are available, making the comparison of different loop geometries and various boundary conditions an impossible task. Hence a novel investigation has been undertaken which focuses on the unification of NCL modeling based on unified definition of characterizing parameters. A general set of governing equations has been developed and appropriate definition of all relevant dimensionless groups and reference parameters has been identified. A Proper choice of reference temperature drop has been suggested so that different heat input modes can be simulated without disturbing the basic structure of mathematical model. Applicable friction factor and heat transfer correlations have also been identified with proper definition of unified characterizing parameter. Analytical solution for a few representative loops under steady-state condition is developed and compared with a number of available experimental studies. Excellent degree of matching has been observed for all of them. Loops having identical geometry but different modes of heat input exhibit similar nature of steady-state solution, thereby signifying the success of such unification. (C) 2013 Elsevier Ltd. All rights reserved.