Size changes of the brain is monitorized for clinical or research purposes. Stereological methods provide some techniques to obtain quantitative information about the size of the brain or size relation of its components within the whole. The Cavalieri principle is the main technique to estimate the volume of brain and its components. Using this technique, the volume of any object could be estimated from a set of slices through the object, provided that they are parallel, separated by a known distance. The cut surface areas of the sections are assessed and the multiplication of the total cut surface area with the mean of the section thickness provides an estimation of the volume of the examined object. The point-counting and planimetry are two methods for the assessment of sectional cut surface areas in the Cavalieri principle. Sometimes, the volume of brain could not provide comparative information among the groups. Scientists have documented several factors that contribute to the size of brain. Factors related to brain growth, such as gender and physical size, are thought to influence the maximal size of an individual’s brain. Comparing solely the brain volumes or its components between two groups will not provide reliable data. At this point, the volume fraction method of stereological approaches proposes the solution. The volume fraction is simply expressed as the fraction of component within the reference volume. Both methods could be used digitally or they can be applied on the printed films. There are many studies describing the techniques and its applications. However, mostly they contain advanced information that is not suitable to be digested by newcomers. In the present paper we gave simple information on the application of both techniques. We also discussed the factors affecting the volume estimations on radiological images. Examples of applications and their solutions are also provided.

brain, volume, volume fraction, stereology, the Cavalieri principle, imaging, magnetic resonance, computed tomography