mySHOEFITTER is a scientifically based, biometric foot measurement technology for mobile devices (e.g. smartphones, tablets), which enables users to easily size feet with millimetre accuracy to consequently determine the exact fitting shoe size for the respective shoe model during the online ordering process. The use of mySHOEFITTER does not only work against the massive problem of rising shoe returns in the e-commerce environment and helps to maximize profits, but also improves sustainability by avoidance of CO2 emissions, packaging material and destruction of returned shoes. Our application is the world's only functioning smartphone measurement technology which measures the customer's feet with a deviation of max. 2mm in length and width. In addition, our AI algorithm learns from each return and makes the measurements and size suggestions more and more accurate. The problem of extremely inconsistent shoe sizes and insecure customers, which has existed for more than 200 years, is finally solved.