Introduction: This study examined what methods people use to determine and interpret their body weight, and what factors are associated with either an underestimation of overweight or an overestimation of a healthy body weight. Method: The study used self-reported data on weight and height. Data were collected by means of questionnaires (n = 722). Results: In comparison with unaware overweight individuals, aware overweight respondents had a significantly lower score on comparing their body to that of others and on listening to remarks from others as methods to determine and interpret their body weight. The same was true for respondents with a correct perception of their healthy body weight compared with respondents who overestimated their healthy body weight. Respondents with a correct perception also had a significantly lower score on using the need to change to a different clothing size to determine body weight. Underestimation of overweight was significantly associated with body mass index (BMI), intense physical activity, knowledge of a healthy weight range and body comparison; overestimation of healthy body weight was significantly associated with gender, BMI, weight loss history and media influences. Discussion: The study had a cross-sectional design, and therefore no causal relations could be determined. Despite this, the study provided more insight into the way people estimate and judge their body weight. © 2006 The British Dietetic Association Ltd.