Adult numeracy is one of the essential skill sets to navigate through numeric information-rich labour markets in general, and STEM industries in particular. Yet, relatively little is known about how numeracy skills are used in different settings in the USA. This study examined numeracy skill use patterns of STEM and non-STEM workers at work and home. Data were obtained from the 2012/2014/2017 Program for International Assessment of Adult Competencies, USA restricted-use file. Adults who were employed and aged between 25 and 65 years old (n = 5,220) were included in this study. Latent class analysis revealed four numeracy skill use patterns: non-users, non-occupational (i.e. at home) simple numeracy users, ubiquitous numeracy users, and occupational numeracy users. Additional multinomial logistic regression analysis showed that the STEM occupation was associated with a greater likelihood of being ubiquitous users than being non-occupational simple users. Results also showed that numeracy proficiency, socioeconomic statuses (i.e. educational attainment and income), as well as demographic characteristics (i.e. gender and race/ethnicity), were predictive of the numeracy skill use patterns in terms of the level of engagement and settings. Findings from this study inform policies and interventions which promote skill engagement and improvement among workers in the USA. [For the corresponding grantee submission, see ED624035.]