Food waste is a major problem that must be reduced in order to achieve a sustainable food supply chain. Since food waste valorisation measures, like energy recovery, have limited possibilities to fully recover the resources invested in food production, there is a need to prevent food waste. Prevention is most important at the end of the value chain, where the largest number of sub-processes have already taken place and occur in vain if the food is not used for its intended purpose, i.e. consumption. Catering facilities and households are at the very end of the food supply chain, and in Sweden the public catering sector serves a large number of meals through municipal organisations, including schools, preschools and elderly care homes. Since the first step in waste reduction is to establish a baseline measurement in order to identify problems, this study sought to quantify food waste in schools, preschools and elderly care homes in one municipality in Sweden. The quantification was conducted during three months, spread out over three semesters, and was performed in all 30 public kitchen units in the municipality of Sala. The kitchen staff used kitchen scales to quantify the mass of wasted and served food divided into serving waste (with sub-categories), plate waste and other food waste. The food waste level was quantified as 75g of food waste per portion served, or 23% of the mass of food served. However, there was great variation between kitchens, with the waste level ranging from 33g waste per portion served (13%) to 131g waste per portion served (34%). Wasted food consisted of 64% serving waste, 33% plate waste and 3% other food waste. Preschools had a lower waste level than schools, possibly due to preschool carers eating together with the children. Kitchens that received warm food prepared in another kitchen (satellite kitchens) had a 42% higher waste level than kitchens preparing all food themselves (production units), possibly due to the latter having higher flexibility in cooking the right amount of food and being able to chill and save surplus food. The large variation between kitchens indicates that they have different causes of food waste, but also different opportunities to reduce it. Detailed waste quantification for each kitchen can therefore be the first step in the process of waste reduction.