This application named ‘Object Size Detector’ version OSD_2021 (64-bit) was developed within 2 weeks. The purpose of building this application is to detect the measurement of object in real time. Python is the language used and the application is coded in object-oriented programming style with three main class: ‘ObjDetector_main’, ‘ObjDetector_cv’ and ‘ObjDetector_UI’. Qt is used as Graphics User Interface(GUI) for this application while the main library used for image detection is OpenCV with the aid of scikit-image for edge thinning and KMeans clustering from scikit-learn. Other than that, library such as numpy, imutlis, math, time, os, random and sys are used to assist the application.