The size of Zr is very similar to

Zr and Hf belong to the fifth and sixth period respectively of group 4 in the modern periodic table. Even after the addition of a new shell in Hf, the atomic radius of Zr is almost the same as that of Hf because of lanthanoid contraction.

Atomic radius of Zr and Hf is 206 pm and 208 pm respectively. Even though a new shell is being added to Hf, the size of both of them is almost the same which is not true for s and p block elements. Introduction of a new orbital always leads to an increment in the size of the atom which is not being observed here.
Thus, Zr and Hf have similar properties though they lie in different periods.