Food waste has far-reaching effects on the global population and thus has been given significant attention in United Nations Sustainable Development Goals. An increased generation of food waste at the consumer level due to online food delivery (OFD) systems has been a topic of research attention. The present study empirically investigates the impact of vagueness in plate size information on OFD apps on the food waste behavior of consumers and potential underlying psychological mechanisms involved in the online food ordering process. Through a 2 × 2 experimental design carried out in India, the causal effect of the vagueness in plate size information on food waste is examined through the mediating roles of anticipated shortage and over-ordering. When consumers anticipate a food shortfall due to vagueness in plate size information, they prefer to order more than needed, which eventually leads to higher food waste (FW). The theoretical and practical implications of the study are discussed.