There has been no clear indicator to determine if a project has experienced schedule acceleration or not. Schedule acceleration occurs when a contractor is required to do a certain amount of work in shorter period of time than the normal experienced time or optimal time typical for the type and size of project in a given set of circumstance, or to do more works in a given time frame. From this fundamental aspect of schedule acceleration, the concept of Workload Ratio was developed. Workload Ratio can be considered as a measure to represent if the project schedule has been accelerated or not, and how much the project was accelerated. Workload can be understood as the amount of works a contractor or a subcontractor should perform in a certain period. By dividing actual weekly workload by planned weekly workload, Workload Ratio can be obtained, where Workload is defined as total man-hours divided by project duration in week. To determine the impact of Workload Ratio on construction labour efficiency, the relationship between Workload ratio and labour efficiency were quantified by analyzing 96 projects collected from sheet metal and mechanical contractors across the United States.