Aesthetics is crucial for product design and success, yet there are no differentiated and validated evaluation tools for the assessment of interactive products (e.g. IT products, household appliances, home entertainment devices or power tools). This contrasts with the significant efforts invested in the development and optimization of such products. To close this gap, we developed and validated the Product Aesthetics Inventory (PAI) and its short version PAI-S through three studies (with a total of > 7,000 respondents). In a pre-study with design experts (N = 6) and product users (N = 4), we developed the initial item set. This set was then used by 6,002 participants in an online survey to evaluate household appliances. In Study 1, data from 3,000 participants helped determine the number of factors for product aesthetics using factor analysis. Study 2 verified this structure with the remaining 3,002 participants, confirming construct validity with established aesthetic scales, intentions and general judgements. Both studies demonstrated strict measurement invariance across four household appliance categories, underscoring the psychometric quality of the scales. Study 3 (N = 1,028) extended these findings to power tools, office equipment and consumer electronics, affirming reliability, validity and measurement invariance for most PAI dimensions. The final PAI has 32 items measuring eight dimensions: visual aesthetics, operating elements, brand logo, feedback sounds, operating sounds, haptics, interaction aesthetics and impression. An overall product aesthetics factor can be assessed with the PAI and the 8-item short version PAI-S. This article also presents advances in scaling approaches for the PAI and PAI-S, along with practical benchmarks for three broad product categories, offering valuable guidance for the application and interpretation of product aesthetics assessments.