3-4. The weight of a purple potato is between 12 and 2 grams, 1 kg =5 grams, and each purple potato is different in size. If you make more than 5 grams, you can have 4 purple potatoes, at least 3 purple potatoes. Purple sweet potato is a panicum miliaceum belonging to the genus Ipomoea of Convolvulaceae. Simple leaves alternate, and the leaves are heart-shaped and chicken-claw-shaped.