Does penis size matter with the Clone-A-Willy? In a word: No. The Clone-A-Willy kit is designed to replicate most men up to 9 inches without needing extra material. It's a very rare man who's over 9 inches long when measured along the top of his erection. Obviously every man is a little different, and if you're trying to copy a 7 inch penis with an extra thick 2.5+ inch diameter (7.8+ inch circumference), you might not have enough silicone to fill the mold you've created. So, if you're one of the scarce few men who might need extra material to fill their mold, do you need to purchase two kits to get a full-size replica? Again: No. A less expensive way to fill the mold is to purchase a 7 inch vibrator for $6.95. It will displace more silicone than the 5 inch vibrator that comes with the kit, thereby filling the mold of the exceptionally large gentleman.