Tumor cancer is one of the dangerous cancer diseases and can cause a large a mount of death every year all around the world. Normally tumor cells are of two different types, they are mass and malignant. Their detection is always requires special attention for the researchers in field of image processing. Image segmentation is one of most important and fundamental approaches of digital image processing and wid ely being used for the specific suppose of detecting and measuring the size of tumor in the human body. This paper represents the extensive Segmentation algorithm to tumor Detection and measuring from MR Image using segmentation. First, an input image is converted into fixed size then prepossed by Gaussion law pass filter which is improve the qulity of an image. Then the image is segmented using the thresholding method in which by selecting the threshold value an image is segmented. Then using region of interest the segmented image is cropped and then after measuring the size of segmentation image using pixels for the tretment planning. And also there is post processing for morphological operations. This algorithm is much simpler and less complex in the calculation. Keywords--Magnetic resonance Imaging, brain tumor, Area calculation, ROI, thresholding, Ga u ssi a n l a w p a ss fi l t er, ero si o n and d i l a t i o n .