Please bear with my lengthy answer.
In your question you imply that you believe or have assumed that there is a soul, is it not? Basically they are the same, belief and assumption; that is, they both pre-suppose something to be so. But it is never the same as one’s direct experience, that, such and such, is a fact. One believes in one too many things without ever questioning if it is infact so. One has heard, read, been told, from a very early age about so many things, that one loses track. One simply hasn’t the time or the energy to analyse and explore for oneself whether all of what one has come to believe in so fiercely, so passionately, are factual or not. The belief one holds onto so vehemently from so young an age, becomes so deep rooted, that in time, one takes it for granted to be so, it has to be. And then one goes on to defend and declare war in the name of beliefs, that one has never had any direct experience of. Is this not the case, in the world? History tells us of many a, bloody battles fought between the good and the evil, only, the one fighting always believes he is on the good side, whether it is the self or one’s opponent. And history continues to dictate our values and all our actions, and it will continue to be, until, we, as a society, that is, each and every one of us being this society, stops and questions everything that we have come to believe to be so, without actually knowing it to be so.
So, when one asks what the size of a soul is, there is implied in that question, that soul exists. If it does, whose soul is this question being directed to? Yours, or, another’s? Or does one relate to the notion of soul with something cosmic that exists, and which must continue to exist, that death cannot touch? If it is your soul, then one ought to know for oneself, the size, proportion, and measurement for oneself, surely. But if one has asked the question, surely, it is out of not knowing for oneself. One doesn’t know whether the soul is personal, impersonal, cosmic or whatever, to begin with. One has no idea whatsoever about soul, yet one assumes that it is there, is it not? Why? It may be there or it may not even exist, to begin with. But must one not begin with this enquiry for oneself, first and foremost?
Does soul exist? To understand if something exists, one must first understand what it is, it’s very structure, its foundation, etc. When one questions what something is, in that very questioning one unravels for oneself many a truths about that very thing that one investigates, is it not? So, what is soul? Does it belong to the self? Or is it something that exists outside of it, and therefore cannot be touched by the self? If it cannot be touched by the perishable self, then is it imperishable? What distinguishes the self from the soul? Is there a difference? Or, are they both one and the same, only with different terms, such as, self and soul, jivathma and paramatma, individual soul and cosmic soul, etc? If they are one and the same, what makes one perishable and the other imperishable? Is it possible for one thing to be both living and dead? That is, can something be both mortal and immortal? It cannot because then by mutual exclusion, they will cancel out each other, is it not? That is, a thing can be either living or dead, it cannot be both, can it? It is one thing, whether it is living or dead, not two things, isn’t it? So, if the soul and the self are one and the same, is it eternal or is it perishable? Does one’s soul perish upon the death of one’s physical body? If it does, then soul is quantifiable as a physical measure. And if so, then it must be a physically tangible thing just as one’s physical body is, is it not? It must be actual physically, just as one’s physical body is. Therefore, one must be able to touch it and see it, just as one would one’s physical body or the world of physical objects.
If one asserts that soul is not tangible physically, then it is implied that, therefore, it has nothing to do with the physical body, is it not? If so, upon the death of one’s physical body, which is made of matter, who is it that dies? If soul has a life of its own, which is untouched by physical death, and therefore, eternal, does it merely occupy a physical body to experience life? Why? Why does it need to occupy anything at all if it has a life of its own? Is it that being intangible, it needs a tangible form to have tangible experiences? Is it the experiencer then, the enjoyer, the feeler, etc., in every physical experience that one has in one’s life? That is, while the physical experiences themselves are tangible in one’s life, the corresponding feelings that it triggers in oneself are intangible, is it not? When there is physical injury, one is physically in pain, which are both tangible, but when there is an emotional injury, there is suffering at an emotional level which is intangible. Likewise, when one has accomplished something, there is an inward sense of achievement, of joy, of success etc., all of which are intangible. Can it be said therefore, that these intangible inward feelings, and sensations are attributes of the soul or what one thinks of as the self? Without these attributes, what is a soul? And what purpose might it serve? Conversely, can the physical body come to life merely as matter, without a soul residing in it? Does it need a soul to reside in it?
Is physical matter capable of experiencing, feeling, emoting, enjoying the various experiences in one’s life, purely as a life form made of matter alone? The human brain triggers physical and chemical reactions to the external world of stimuli, but one has never been able to pinpoint exactly where in the brain, do, intangible inward psychological feelings arise from. Hence, one has instead created a soul, a super sacred entity, and has further created a myriad, classes and divisions in it, such as an individual soul, cosmic soul and then there is the supreme soul, and made it so tremendously important, that it has never been questioned ever. The human mind has been so rooted deeply in this sacrosanct entity that they never question it.
In any organism, matter is needed to both build and sustain the organism. We are made of matter in solid, liquid and gaseous forms, afterall. Life is composed of and interacts with matter in these three states. If one asserts that soul is energy and life forms need energy, then matter is conserved just as energy is. Atoms and molecules represent stored energy. Does this mean matter and soul are one and the same? Can it be one and the same? If it can, then soul is perishable and therefore, measureable. What makes one assert that soul is energy? It may or may not be but one must begin by questioning the very structure of it, is it not? Only then can one discover for oneself.
The cosmos and the universe, which is made up of the fourth state called the Plasma, is a living organism too. There is the birth and death of stars, and the universe continues to expand. But there is a certain good order in which it operates, is it not? Suppose it weren’t to function in its orderly rhythm for a day, because it felt bored of its monotony, what would happen? Like so, is it possible for a human life, to function in an orderly rhythm, purely as a life form made of matter, without convoluting itself to be something more than what it actually is? To find out, the human mind must be capable of facing the fact of what it is, is it not? Can one actually accept the possibility of being nothing more than a physical and chemical reaction in the brain? Can one actually come face to face with it, without any pre-conceived notions of Soul, Atma, Parabrahman etc, that one might become once the ego is removed? The Soul is the ego. They are one and the same, afterall. It is for the soul or the self to feel alive, to feel important, to feel pride, to feel pain, to suffer, to believe, etc. And it is in all of these, that the self comes alive, is it not? Without these, what is left of any inward psyche to attribute to the self or the soul? And without any inward intangible psychological entity, surely, there cannot be any psychological discords in oneself, that is, the conflicting opposites of likes and dislikes, love and hate, violence and harmony, peace and conflict etc. Once there is the distortion of reality, surely there is bound to be, a myriad further distortions too. But when there is none, and one can face the fact of oneself, as a life form, that exists just as any other living organism, what would be the state of such a mind? A mind that has no notions, concepts, beliefs, is a mind that is free, is it not? Free from fears, anxieties, insecurities, greed, violence, pride, hatred, anger, it thereby has no notions, or concepts, of courage, security, non-violence, harmony, humility, love and so on. Such a mind is always in the present, it meets the new as new, and therefore, alive. Only such a mind lives in the knowing, in the Truth in every moment, in every experience, in every activity, and therefore, only such a mind can come upon that which always is, the eternal.
There, surely, is an intelligence behind, and in everything, it is not a belief, it is not an assumption, it is so. It is that which is eternal. When a pendulum oscillates, it not just swings in one direction alone, it goes in the opposite direction too. For every action, there is an equal and opposite reaction, is it not? That is the law in which the universe operates, as do all life forms. If there is such a thing that perishes, there must be something that doesn’t. Surely. If the universe, the cosmos, and, all its life forms, are fleeting and transient, then there must be something which is eternal. It is that which always is.