D is for diameter
Normal moles are smaller in size and usually don’t grow bigger than 6 millimeters. On the other hand, melanoma moles tend to grow in size and can be larger than 1/4 inch. However, having a bigger size is not a hard and fast rule for the diagnosis of melanoma. A cancerous mole can be smaller than 1/4 inch, and a healthy mole can be larger than 6mm.