Previous research on own visual body size estimation has only looked at estimates made by comparing own body size to a test body viewed in third-person perspective. However, people spend relatively little time seeing their body from this perspective as compared to the first-person perspective. Here, we asked whether the visual perspective on the body influences the accuracy of estimating own body dimensions. A three-dimensional virtual test body was presented in life size in immersive virtual reality either from a first- or from a third-person perspective. In a method of adjustment task, participants adjusted a varying number of the test body’s dimensions (weight, leg length, arm span, hip width, and upper torso area) to match their own body. Results showed that participants were more accurate in estimating own body dimensions in the third-person perspective condition, suggesting that our mental body image is informed by viewing the own body as a whole, such as in a full-length mirror.