Why is the mole a unit of measurement?

I really can't understand why is the mole a unit of measurement and not just a constant. I mean, we use units to express things that we can measure but that are not countable, that are continuous - and not discrete. However, the number of atoms (or whatever) of something is clearly countable, discrete. It is also a huge number, which would request for a constant, a number to multiply to: Avogadro's constant is that number, like mega or kilo in SI for other units. We could still write 14 mole, where mole is the Avogadro constant (exactly the way it is), but every book I read so far states that the mole is a unit of measurement, official in the S.I., and so does Wikipedia. It just makes no sense to me that it is considered that way, but there is obviously a reason why... What is it?

• I've been thinking about this question too! Why is "mol" a "Base SI unit" when "radian" is not? Jul 11 '20 at 23:12
• Good question. It got even more confusing since: "The definition of mole was adopted in November 2018 as one of the seven SI base units" :-/ Oct 27 '21 at 14:44

A fundamendal unit is a part of a particular set of units upon which all other units can be derived. In this case, the mole is related to the fundamental unit of mass and is defined as an amount of items equal to the amount of carbon atoms in 12 grams of $^{12}C$.
• Yet this does not answer the main question: why not simply consider the mole as a constant? A mole is certainly not a dimensional unit such such as one representing mass or time... It is just a number, somewhat like $pi$ or $10^{24}$. May 30 '14 at 6:57
Let me add to bobthechemist's answer. The mole counts quantity. The fundamental unit involved is Avogadro's Number, approximately $6\times 10^{23}$. So $6\times 10^{23}$ units of anything is a mole of that thing, whether it is atoms of hydrogen or sand particles.