Charles Ellicott Commentary Exodus 30:2

"A cubit shall be the length thereof, and a cubit the breadth thereof; foursquare shall it be; and two cubits shall be the height thereof: the horns thereof shall be of one piece with it." — Exodus 30:2 (ASV)

Foursquare shall it be. — Of the same shape as “the brazen altar” (Exodus 27:1), but much smaller—two cubits high instead of three cubits, and a cubit square at the top instead of five cubits. This small space was ample for burning so precious a material, which could only be offered in small quantities.

The horns thereof. — Compare Exodus 27:2, and Note 1, ad loc.

Shall be of the same — i.e., of one piece with the altar, not made separately and then attached to it.