Purpose – The purpose of this paper is to analyse and compare the serving sizes and energy values reported on the nutrition information of all processed and ultra-processed dairy products in their regular and diet/light versions available for sale in a large supermarket in Brazil. Design/methodology/approach – A check was done for associations between the compliance of reported serving sizes, energy values per serving and energy density for regular foods and foods advertised at “diet/light” (with reduced fat and calories). Findings – The data included information from 451 dairy product labels. Most of the products had serving sizes smaller than the reference set by Brazilian law. A high variability of serving sizes was found for similar products. “Diet/light” foods tend to report serving sizes that are even smaller and more inadequate. Moreover, the energy density of these products was similar to that of the regular foods. Smaller serving sizes may be being presented on “diet/light” foods in order to report lower energy values and on similar foods to show non-existent differences in energy values. These results point to the importance of standardizing serving size information on food labels so that consumers have access to clear and accurate information about food products. Originality/value – This was the first census-type study to analyse the serving size information of dairy products at a supermarket of one of the ten largest supermarket chains in Brazil. This work extends the scope of current food labelling and contributes to the discussion about how nutrition labelling has been presented to Brazilian consumers and its possible consequences for food choices and the guarantee of consumer rights.