Q. I live in a condo on the fifth floor; do I have to light the menorah by the window, since it is over 20 amos? Is this measured from the ground of the street or the average height of the eyes of the people on the street?

A. Shaar Hatzion (671: 42) and other Poskim rule that if the menorah is higher than twenty amos from the street below, (9.60 m. following R’ Chaim Noeh, or 11.52 m. according to the Chazon Ish), one should light next to the entrance door. (P’ri Megodim maintains that even when higher than twenty amos, some people in the street will notice, however many Poskim disagree.)
Horav Shlomo Miller’s Shlit’a opinion is that it is measured from the ground and not from the height of the eyes of the beholders walking on the street. (See question 1225 in regards to measuring from the menorah’s body or the flame).

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a