Research on public opinion and international security has extensively examined attitudes toward nuclear weapons, but the diffusion of basic knowledge about nuclear weapons among the everyday citizens has nevertheless been mostly missed. This study proposes a working definition and advances a measurement model of knowledge on nuclear weapons in the general public. It analyzes data from two novel surveys conducted in 2018 (N = 6559) and 2019 (N = 6227) where respondents from Belgium, France, Germany, Italy, the Netherlands, Poland, Sweden, and the United Kingdom answered a web survey on attitudes and factual knowledge on nuclear weapons. Exploratory and confirmatory factor analytic models are used to examine the dimensionality and to assess the measurement invariance of a scale of knowledge about nuclear weapons. A bifactor measurement model, where a strong general factor represents the construct of interest and specific factors account for the presence of testlets due to questionnaire design, is established and validated. Configural, metric, and scalar invariance are established across the eight samples. The findings indicate that knowledge about nuclear weapons in the general, non-expert public can be reliably measured cross-nationally.