Three rapid market estimation techniques were used to quantify the informal milk market in two Tanzanian municipalities, namely Iringa and Tanga, with reference to producer-based estimates, retailer-based estimates and a stratified consumer survey. The nature of the milk market systems in the two study areas was reflected in the magnitude and dynamics of milk consumption; the informal market was particularly important for a ‘subject to deprivation’ group in both cases. Producer-based estimates did not account for milk from outside the study area, whereas retail surveys omitted details of the producers’ own consumption and their direct sales. Consumer surveys captured the widest variety of informal milk sources but, like retail studies, omitted producers’ consumption. Therefore the most accurate rapid estimation of markets for consumable products may be obtained by triangulating producer data with consumer surveys (informal market) and adding reliable (and usually relatively easily obtained) data from processors and retailers to capture trade through formal channels.