On the way to automated layout planning numerous challenges must be faced. One of these challenges is the automated layout evaluation, which can be considered as the core of automated layout planning. The research field of factory planning differs from related research topics such as facility layout planning (FLP) from operations research (OR) by focusing for example on qualitative criteria in the evaluation. However, findings on how qualitative criteria can be interpreted in a quantifiable and measurable way are still rare. In this article, we address these questions with a focus on changeability, which can be regarded as the most important qualitative evaluation criterion in layout planning. For this purpose, a survey was conducted that aims to determine changeability from the understanding of industry experts and to define it consistently with the understanding from literature. Based on this understanding, performance metrics are derived to measure the layout changeability.