The steel fabrication and installation works in a steel-structured building project account for 20% of the entire construction cost. In estimating construction costs, a few parameters are more significant than work item productivity. However, the Standardized Productivity (SP) of steel works presented in Poom-Sam, which is the standardized estimating guide system used in the public sector in Korea, has rarely been updated since its establishment in the 1970s. In order to update and improve its structure and figures, 15 construction sites and 5 steel fabrication shops were visited over a period of two years. From the study, it was found that the structure of Poom-Sam was rather complex and outdated and that the average SP of the works analyzed from the research was approximately 85% of the current SP. Moreover, the effect of the productivity differences on total construction cost was approximately 10%. The productivity improvements and amended Work Breakdown Structure (WBS) are attributable to the technology advancements in equipment and construction methods over the past two decades. The results of this study will improve the reliability and accuracy of cost estimation in steel works.