What is mass ?? Text books define it as the "amount" of substance... You can also use some equations and toss Mass out, giving other definitions. But my question is about the wording "amount of substance" > What is this "amount of substance" ? > Because "amount" refers to counting.. How can you count this "substance" ? > I know that mass of a cube of butter is not the amount of sub-atomic particles that butter has... then what is it ??? > Some humans have spread the thought that the number & unit 1Kg, refers to the idea of the stuff kept here This means the amount of matter present in 1KG of butter is same as the amount of matter present in the reference Platinum-Iridium Alloy. ??? How should I digest the concept ? How can I compare Butter & the Pl-Ir Alloy > I am fed up of circular definitions where for eg. Mass can be defined in terms of Force, accel, etc. ..and Force in turn will be defined interms of Mass, accel etc.