Alzheimer's is one of the most common types of dementia in the world.Although not a contagious disease, this disease has many impacts, especially in socio-economic life. In diagnosing Alzheimer's and using interview techniques, physical examination methods are also used, namely using an magnetic resonance imaging (MRI) machine to get a clear image of the patient's brain condition, with a focus on the hippocampus and ventricular area. In this paper, we discuss the calculation of the volume of the hippocampus, especially the coronal slice, to provide information to doctors in making decisions on diagnosing the severity of Alzheimer's. Using the basis of volume calculations, we made a 3D visualization reconstruction of the coronal hippocampus slice area in order to make it easier for doctors to analyze the condition of the hippocampus area, which in the end will be used as a recommendation in the classification of the severity of Alzheimer's. Our experimental results show, the lower the severity, the bigger the volume, the more slices, and the longer the counting time.