What was the height of the Mizbe'ach?
Rashi #1 (citing R. Yehudah, Zevachim 60a): It was three Amos tall, as the Torah records.
Rashi #2 (citing R. Yossi, Zevachim 60a.): It was ten Amos tall (twice its length). 1
Based on a Gezeirah-Shavah, "Ravu'a" "Ravu'a" from the Mizbe'ach ha'Ketores. And the Torah gives the height as three Amos, because that was the height of the Mizbe'ach (excluding the K'ranos) above the Sovev - a walkway for Kohanim around the Mizbe'ach (Rashi).
Having given the measurements as five Amos by five Amos, why does the Torah see fit to add the word "Ravu'a"?
Refer to 27:1:1:2*.
Oznayim la'Torah: Square is not dependent only on the four sides being equal, but also on the four corners, which must all be at an angle of ninety degrees.
What if the Mizbe'ach was not exactly square?
QUESTIONS ON RASHI
Rashi writes that one opinion holds that the Mizbe'ach was 10 Amos tall. How could the Kohanim put blood on the corners, and wood, limbs and Chelev on the fire on top?
Da'as Zekenim: Even though the Torah does not mention a ramp, we must say that it had one, for one may not ascend the Mizbe'ach through steps.
Shabbos (92a): This opinion must hold that the Levi'im were all ten Amos tall [to explain how they carried it normally, i.e. two thirds below the shoulder. 1 Also the Kohanim are Leviyim!] (PF)