The contrabass saxophone is the lowest-pitched extant member of the saxophone

Saxophone

The saxophone is a conical-bore transposing musical instrument that is a member of the woodwind family. Saxophones are usually made of brass and played with a single-reed mouthpiece similar to that of the clarinet. The saxophone was invented by the Belgian instrument maker Adolphe Sax in 1846...

 family proper. It is extremely large (twice the length of tubing of the baritone saxophone

Baritone saxophone

The baritone saxophone, often called "bari sax" , is one of the largest and lowest pitched members of the saxophone family. It was invented by Adolphe Sax. The baritone is distinguished from smaller sizes of saxophone by the extra loop near its mouthpiece...

, with a bore

Bore (wind instruments)

The bore of a wind instrument is its interior chamber that defines a flow path through which air travels and is set into vibration to produce sounds. The shape of the bore has a strong influence on the instruments' timbre.-Bore shapes:...

 twice as wide, standing 1.9 meters tall, or 6 feet four inches) and heavy (approximately 20 kilograms, or 45 pounds), and is pitched in the key of E, one octave below the baritone.
The contrabass saxophone was part of the original saxophone family as conceived by Adolphe Sax

Adolphe Sax

Antoine-Joseph "Adolphe" Sax was a Belgian musical instrument designer and musician who played the flute and clarinet, and is best known for having invented the saxophone.-Biography:...

, and is included in his saxophone patent of 1846, as well as in Kastner's concurrently published Methode for saxophone.