A design system generates a design for an in-ear device customized for a user. The in-ear device produces audio content for the user. The design system captures anthropometric data of the user. Using machine learning techniques, the design system determines features of an ear of the user from the anthropometric and generates a three dimensional (3D) geometry of the user's ear. A design for the in-ear device is generated based on the 3D geometry of the user's ear and includes a shell configured to fit in at least a portion of an ear canal of the user.