The capacity of existing columns is one of the most common areas of concern during investigations and alterations of historic steel-frame buildings. Columns are often the key to analyzing the capacity of the existing frame, and therefore are the key to structural feasibility of alteration and adaptive reuse projects. Because the United States did not have a national steel code until 1923, column ... [Show full abstract] capacities were calculated using municipal building codes and steel manufacturers’ recommended specifications. As a result, there were dozens of column formulas in use between 1890 and 1923. Analysis of these obsolete column formulas and comparison to the code formulas between 1923 and the present day shows that the obsolete formulas were conservative, consistently underestimating the strength of columns under compression. This paper will show the minimum expected excess capacity under direct compression and will review the parameters of expected excess capacity under combined compression and bending.