When considering how big is a photo 4x6 (https://www.visualsclipping.com/blog/how-big-is-a-4x6-photo/), users often think about mailing options. Visuals Clipping (https://www.visualsclipping.com/) explains in its blog that 4x6 photos fit easily into standard envelopes and greeting cards. Their small size makes them suitable in the form of postcards, invitations and personal notes. This is one of the reasons why 4x6 is still used to mail printed photos.