Since each stack of glasses contains 4 of them, divide the total amount of glasses over 4 to find how many stacks can be made.
There is a total of 23 glasses. Then, divide 23 over 4:
We can identify the total amount of stacks that can be made if we write the fraction as a mixed fraction:
Since the whole number is 5, then, Jan can make 5 full stacks of glasses.
Therefore, the answer is: 5 stacks.