This paper is a contribution to the Impact Project in the area of software resource estimation. The objective of the Impact Project has been to analyze the impact of software engineering research investments on software engineering practice. The paper begins by summarizing the motivation and context for analyzing software resource estimation; and by summarizing the study's purpose, scope, and approach. The approach includes analyses of the literature; interviews of leading software resource estimation researchers, practitioners, and users; and value/impact surveys of estimators and users. The study concludes that research in software resource estimation has had a significant impact on the practice of software engineering, but also faces significant challenges in addressing likely future software trends.