An important macroscopic arc parameter, describing its complex nature is the arc resistance. It can be easily calculated by using the well-known Warrington formula. Authors investigated the results of Warrington's tests. By taking into account the conditions under which they are obtained (e.g., inaccurate measurement devices), it is unquestionable that these results are today highly empirical and not accurate and general enough. Laboratory testing provided in the high-power test laboratory FGH-Mannheim (Germany), in which long high current arcs are initiated, was the basis for the research results presented in the paper. Based on the analysis of laboratory-recorded arc voltage and current waveforms, the new arc model is derived. An example of arc computer simulation using the new model is given. Based on the new arc model, a new approach to arc resistance calculation is presented. The new formula for arc resistance is compared with the old Warrington formula.