Well,
according to the book Sextrology here is the alleged size run down:
Aries
"His penis tends to be of avereage to ample length, though rather thick and stick straight, th ehead of which may also in in a markedly sharp point. His balls, though plum sized, are typically held tight."
Taurus
"Down below, this boy is big, boasting one of the healthier sized cock and bulls ever to be unzipped in the zodiac. Taurus man's package tends toward the loose and low slung sort..."
Gemini
"Even the potential averageness of his package seems engineered to attract women who might be put off by either extreme..."
Cancer
"... like his body, his penis size hovers somewhere around average. Still the crab guy does ten to be rather thick in this area: his balls though not often the low hanger variety, do err on the large size."
Leo
"...his package is similarly designed,as Leo is rarely one to be seriously lacking in that department- not overly hung but considerably thick. His Cojones to share the outsized quality of his other extremities."
Virgo
"Much to his delight, Virgo tends to be amply endowed, generally enjoying and above average length and circumference thqat measures nearly as much..."
Libra
"His private parts are rather textbookin nature, as he's amply endowed though rarely overly so, with bits and pieces as user friendly in appearance as he is- all pink and prettily formed never distinctly dark or deviously shaped in any way."
Scorpio
"...and Scorpio doesnt rule the sex organs for nothing: This boy tends to be healthier than most in this area: his serpent is generally thick, mighty long and heavily veined as are all of his extremities..."
Sagittarius
"... though this stallion hasnt cornered the market on magnitude in the penis department, Sag's overall athleticism suggest a tireless roll in the hay."
Capricorn
"His package thends to be loose and floppy, boasting a rather fleshy phallus as well as low- hanging cojones a signal of an inherent sense of calm..."
Aquarius
"...though Aquarius generally fills out his speedo just fine the bulk of his bulge is again often based in his often jumbo balls..."
Pisces
"He has a loose and floppy basket, though he's pretty averagely endowed, his dick being perfectly proportioned...:"