Answer:
Assuming each of the smallest squares (i.e., each of the 16 ones forming the large square) has a side 1 unit long:
There are 16 squares that are 1x1.
There are 9 squares that are 2x2.
There are 4 squares that are 3x3.
And there is 1 square that is 4x4.
So the total number of squares is 30.