The aim of this study is to construct a measure of numeracy skill use in the workplace for incarcerated and household adults. The 2012/2014 Programme for the International Assessment of Adult Competencies (PIAAC) Survey of Adult Skills asked about the type and frequency of numeracy tasks performed as part of one's job to nationally-representative incarcerated and household adult samples. This paper takes these items from this survey and focuses on the validation of a measure of numeracy skill use in the workplace using the principles of the Rasch rating scale model. In the interest of exploring options for strengthened validity, response categories were collapsed to produce an optimal categorization structure. Findings suggest an instrument to measure numeracy skill use in prison and free market workplaces could potentially be improved with fewer response categories and more items that ask about a broader range of numeracy skills.