Length

Sounded pitch is a direct function of length. Strictly speaking, a baritone to low Bb would be double the length of a alto to Eb, and four times the length of a sopranino to Eb. Minor variations of total length would come from mouthpiece style.

The low A on my baritone (Yamaha YBS 62) adds about six to seven inches of length to the horn over a low Bb instrument. Bear in mind that you are dealing with the sound coming out of a tone hole for the one note (low Bb on a low A horn) and out of the bell on the other (low Bb coming out of the bell on a low Bb horn). Sort of apples and oranges as far as exact measurement is concerned.

I've seen total tube lengths for each instrument listed out somewhere, but I don't recall where. It might have been in a translation of one of the Sax patents. Regardless of the length of the alto and tenor in exact terms, yes they are in proportion to the rest of the instruments.

Finally, as a general rule[/i] the tube size increases as you move up the saxophone family. There are some bore differences between different styles of horns, but the proportions set by Sax were part and parcel of the instrument family, which he conceived as just that.