Ezekiel 43:16
Now the altar hearth is a perfect square, 21 feet long and 21 feet wide.
Exodus 27:1
"You are to make the altar of acacia wood, seven feet six inches long, and seven feet six inches wide; the altar is to be square, and its height is to be four feet six inches.
Exodus 38:1-2
He made the altar for the burnt offering of acacia wood seven feet six inches long and seven feet six inches wide -- it was square -- and its height was four feet six inches.
2 Chronicles 4:1
He made a bronze altar, 30 feet long, 30 feet wide, and 15 feet high.
Ezra 3:3
They established the altar on its foundations, even though they were in terror of the local peoples, and they offered burnt offerings on it to the Lord, both the morning and the evening offerings.