Exodus 27:1

ועשית את המזבח וגו׳ ושלש אמות קמתו AND THOU SHALT MAKE AN ALTAR etc. AND THE HEIGHT THEREOF SHALL BE THREE CUBITS — These words should be understood as they are written (i. e. to mean exactly what they say — that its height was three cubits); this is the opinion of R. Jehudah. R. José, however, says: it is stated here, “[the altar shall be] square” and it is stated with reference to the inner (the golden) altar, (Exodus 30:2) “square [shall it be].” How was it there (in the case of the latter)? Its height was twice its length (“a cubit the length thereof, and a cubit the breadth thereof, . . . and two cubits the height thereof”)! So, also, here: the height shall be twice its length, i. e. ten cubits. And if you ask, how, then, do I explain the words and three cubits the height thereof?” I reply that this gives the measurement from the edge of the surround (סובב) upwards (whilst 10 cubits was the actual height from the ground to the top of the altar) (cf. Zevachim 60a; Rashi on v. 5).

וְעָשִׂ֥יתָ אֶת־הַמִּזְבֵּ֖חַ עֲצֵ֣י שִׁטִּ֑ים חָמֵשׁ֩ אַמּ֨וֹת אֹ֜רֶךְ וְחָמֵ֧שׁ אַמּ֣וֹת רֹ֗חַב רָב֤וּעַ יִהְיֶה֙ הַמִּזְבֵּ֔חַ וְשָׁלֹ֥שׁ אַמּ֖וֹת קֹמָתֽוֹ׃

And thou shalt make an altar of shittim wood, five cubits long, and five cubits broad; the altar shall be foursquare: and the height of it shall be three cubits.