There are currently no industry accepted methods for calculating sealing effectiveness of flange connections at the research and development phase of a project. As there are many different designs of bolted piping connectors being widely used in the oil and gas industry, operators and regulators could benefit greatly from a more accurate comparison and estimate of expected flange tightness level, based on design calculations only. This paper will propose a new methodology for sealing effectiveness estimation of bolted connections based on leak rate calculations. The methodology will combine practical simplicity and advance theory to get a simple but effective engineering/designing tool to assess the seal tightness. A new proposed method will be based on the contact stress pattern (FEA results), material properties (code specification) and surface finish/roughness (manufacture requirements) as inputs and leak rate estimation as an output. The Representative Surface Element concept will be introduced and presented. In this paper, the general methodology principles will be presented and followed by an engineering example.