Abstract: A method for determining a footwear size based on a 3D foot size is provided. The method may comprise: (a) providing a sock with multiple visual reference markers; (b) obtaining, with aid of a user device, an image data of a foot covered by the sock, wherein the image data comprises at least one of the multiple visual reference markers; (c) generating a 3D model of the foot using the image data; and (d) determining a footwear size based on the 3D model of the foot or one or more foot size parameters extracted from the 3D model of the foot.