ABSTRACT Objectives: to construct and validate an instrument for the classification of mother-baby binomials that subsidizes personnel Staffing in in-rooming units. Method: methodological study. The construction was based on theoretical and legal references. Content validity was performed by experts through the content validity index measurement. Then, the instrument was applied to a sample of 122 binomials, and exploratory factor analysis was performed using the principal components analysis. Results: the instrument consisted of seven care indicators: Birth route; Maternal morbidity; Neonatal morbidity; Breastfeeding; Social aggravating factors; Care guidance; and interaction and bonding. All with content validity index of 1. The construct was composed of 3 domains, with Cronbach’s alpha of 0.62, 0.85 and 0.89. Conclusions: the classification instrument of mother-baby binomials allows the classification of mother-baby binomials and may support personnel Staffing in in-rooming units.