The construction industry is known to have several inadequacies leading to cost and schedule overruns. One of the popular methods that attempts to eliminate these inadequacies is lean construction, which is a set of principles and tools that aim to maximize value, eliminate waste and optimize efficiency. The success of lean construction depends on several factors. In other words, implementing lean construction tools does not guarantee reduction in cost and time overruns. There is a gap when it comes to identifying the factors that support the success/failure of implementing lean construction tools. In addition, the literature lacks a scoring system for measuring lean implementation. The goal of this research is to fill the abovementioned gap through developing and benchmarking a scoring system that utilizes lean principles to evaluate the "leanness" of construction projects. To this end, the authors: (1) identified the key factors that influence the leanness of construction projects; (2) determined the relative importance of the identified factors through an expert-based survey; (3) developed a scoring system called "the construction leanness score" for measuring lean implementation; and (4) benchmarked the leanness score representing the industry's performance through collecting data from 30 construction projects. Results indicate that there are 27 key lean factors affecting the efficiency of lean implementation with the top two factors being early involvement of key stakeholders and trust between parties. The developed leanness score is considered the first of its kind to link leanness factors to project performance. Also, the developed benchmarking scale enables companies to compare their level of leanness to that of other companies in the industry. With this, companies are able to benchmark their performance, pinpoint the areas of weaknesses and take necessary actions to meet industry practices. Thus, improving the overall quality of construction projects, decreasing overruns.