This cross-sectional survey study explored associations between perceived bodyweight norms, psychological need satisfaction and motivation for weight control among 500 adult residents of two countries with different overweight/obesity prevalence: the UK (63% prevalence) and the Netherlands (50%). A hypothesised model of the effects of descriptive norms (i.e. perceptions of what is typical for most people) and injunctive norms (i.e. perceptions of what is typically approved by others) on autonomous motivation, mediated through basic psychological need satisfaction, was analysed using structural equation modelling. Descriptive norms did not differ between countries, yet UK adults reported a lower-weight injunctive norm. Perceiving higher bodyweights to be normal negatively predicted motivation to manage one’s bodyweight mediated through an undermining effect on psychological need satisfaction. Perceiving higher bodyweights to be normal may have the potential to reduce individual motivation for weight control, but the sensitivity of people’s perceptions to objective differences in overweight prevalence appears limited.