The use of dimensional analysis and dimensionless parameters is very common in the field of heat transfer; nevertheless, the concept of dimensionless finite element formulation has been applied to a limited type of thermofluid problems. This article uses a nondimensional finite element formulation for studying longitudinal composite fins with interface resistance. Two nondimensional governing parameters have been identified, one each for coating and interface, that completely govern the coating and interface resistance effects. The presented results, for the considered range of geometric, material, and operating conditions, permit identification of the limiting values of the two nondimensional parameters for which the coating and interface effects become negligible. It is found that the coating and interface effects are similar for considered constant- and variable-thickness profile longitudinal composite fins over the studied range of nondimensional material, geometry, and operating condition parameters.