Ezekiel 43:16

The altar hearth shall be square at its four corners, twelve cubits long and twelve cubits wide.

Note 12 (long) cubits is approximately 21 feet or 6.4 meters.

And the altar shall be twelve cubits long, twelve broad, square in the four squares thereof.

The altar hearth shall be twelve cubits long by twelve wide, square in its four sides.

And the altar hearth shall be twelve cubits long by twelve broad, square in the four sides thereof.