Broad shrinkage of the hippocampus in the brain is one indication that occurs in Alzheimer's patients. The leading cause is because the primary function of the hippocampus in learning and storing and processing long-term memory. So, in the context of memory, the hippocampus helps process and retrieve two specific types of long-term memory. Alzheimer's disease can shrink in size and change the shape of the hippocampus. This shrinkage in the size of the hippocampus is directly proportional to the severity of Alzheimer's. In this paper, we will discuss the measurement of the hippocampal area on the sagittal slice based on the Clinical Dementia Rating (CDR) scale that standards in measuring the severity of Alzheimer's. The experimental results show that the method we use has an accuracy of 93.3%