<prompt> A giant congenital melanocytic nevus is usually of the size:5-10cm10-15 cm15-20 cm20cm  <response>: American National Institutes of Health NIH consensus definition to categorize naevi as small under 1.5 cm in diameter, large as having a diameter between 1.5 and 20 cm and giant naevi as having a diameter of 20 cm or more. Note: It is also called garment or bathing-trunk naevus. Most common site is lower back. Ref: Rooks textbook of dermatology, Edition-8, Page 54.10. 