[j_s]

In case you are not aware, last fall they doubled the free edition size limit and introduced a $25/month subscription option (eventually the same price at $300/yr).

https://store.xamarin.com/

Xamarin is free for students.

https://xamarin.com/student

[zerr]

How they measure the size actually?

Another important thing - Xamarin.Forms should be in the free edition, if it is aimed for starters.... Big studios or established companies can afford to develop native UIs for each platform separately.