One of the major research directions in robotic vision focuses on calculating the real world size of objects in a scene using stereo imaging. This information can be used while decision making for robots, manipulator localization in the workspace, path planning and collision prevention, augmented reality, object classification in images and other areas that require object sizes as a feature. In this paper we present a novel approach to calculate real world object size using RGB-D image acquired from Microsoft Kinect™, as an alternative to stereo imaging based approaches. We introduce a dynamic resolution matrix that estimates the size of each pixel in an image in real world units. The main objective is to convert the size of
objects represented in the image in pixels; to real world units (such as feet, inches etc.).We verify our results using available OpenSource RGB-D datasets. The experimental results show that our approach provides accurate measurements.