What is the average rate that a human nail grows in a month?

A nail is a horn-like envelope covering the tips of the fingers and toes in most primates and a few other mammals. Nails are similar to claws in other animals. Fingernails and toenails are made of a tough protective protein called alpha-keratin. This protein is also found in the hooves and horns of different animals.

The growing part of the nail is under the skin at the nail's proximal end under the epidermis, which is the only living part of a nail.

In mammals, the growth rate of nails is related to the length of the terminal phalanges (outermost finger bones). Thus, in humans, the nail of the index finger grows faster than that of the little finger; and fingernails grow up to four times faster than toenails.

In humans, nails grow at an average rate of 3 mm (0.12 in) a month. The longest female nails to ever exist measure a total of 601.9 cm. Fingernails require three to six months to regrow completely, and toenails require twelve to eighteen months. Actual growth rate is dependent upon age, sex, season, exercise level, diet, and hereditary factors.