According to the National Council of Teachers of Mathematics (NCTM) (1989, 2000), students at all levels should be exposed to geometry and measurement topics. Standards documents have identified the importance of primary school students selecting appropriate units for measurements in one- and two-dimensional space (NCTM 1989, 2000). This paper provides teachers with an overview of the research regarding students' understanding of one- and two-dimensional units and presents an activity that will help students develop a deeper understanding of the meaning of units in various contexts. This paper is guided by the following questions: (1) What does the existing literature say about students' difficulties with understanding the concept of units involved with various measurements?; (2) What activities have been presented in the literature to provide teachers with tools to develop students' understanding of the unit?; and (3) Based on the literature, what is an activity that can be used to develop students' understanding of the unit? An activity that aims to provide students with an experience that will focus their attention on the unit rather than on the measurements they are attempting to calculate is also presented. (Contains 6 figures.)