Managing pet obesity relies heavily on the active involvement of owners; however, a key challenge arises from misperceptions about their own pet’s body condition. Given evolving societal dynamics like the body positivity movement, understanding owners’ perceptions is increasingly pivotal. To evaluate the differences in owners’ perception, this study compared the use of verbal and visual body condition score scales versus the established nine-point body condition score system. The factors linked to underestimation were further specifically investigated. Owners of healthy adult dogs and cats attending vaccination consultations in Veterinary Hospitals in France between 2020 and 2022 were recruited. They were required to assess their pets’ body condition initially using an oral description and then with the nine-point BCS visual scale. Their assessments were then compared with the BCS determined by veterinary health care personnel, considered the primary investigator. A total of 304 dogs and 270 cats were included in the study. It was observed that 27% of dog owners and 24% of cat owners underestimated their pets’ body condition. Among dog and cat owners, factors associated with the underestimation of body condition were the pets’ overweight status and having children. This discovery emphasizes the need for a holistic One Health approach that prioritizes the health and well-being of both humans and their pets. When it comes to pet owners evaluating their pets’ body condition, underestimation proved to be the predominant misperception. Addressing this issue requires comprehensive education to empower owners to recognize and comprehend their pets’ overweight status, a critical step for the overall well-being of companion animals.