Hilchos Chanukah - Laws of Chanukah
The Mitzvah is to place the candles above 3 Tefachim from the ground and lower than 10 Tefachim. Lower than 3 Tefachim is still okay B'dieved, ex post facto. Higher than 10 Tefachim is also okay B'dieved but higher than 20 Amos is unacceptable
--Shulchan Aruch 671/Mishnah Berurah 27
3 Tefachim according to the Chazon Ish is 11.4 inches. Rabbi Chaim Noeh says 3 Tefachim is 9.6 inches. 10 Tefachim according to the Chazon Ish is 38 inches and Chaim Noeh says it's 32 inches.