At birth a new born's head is approximately what percent of its total body…

Human body proportions change with age according to the cephalocaudal growth gradient: growth proceeds from the head downward, so the head occupies its largest fraction of total body length very early in development, and that fraction steadily shrinks as the trunk and limbs grow faster than the head.

At full-term birth, this gradient places the head at approximately one-quarter — about 25% — of total body length. This is the standard figure used in child-development and growth-chart references for the newborn stage; by contrast, in a fully grown adult the head is only about one-eighth (roughly 12-13%) of total height.

Why the other options do not fit:

• 15% is lower than the newborn ratio — this figure is closer to the head-to-body proportion recorded in later childhood, after several years of faster trunk and limb growth.

• 25% matches the standard newborn figure derived from the cephalocaudal growth gradient, making it the correct answer.

• 40% is closer to mid-gestation fetal proportions, several months before full-term birth.

• 50% is closer to early embryonic proportions, when the head-to-body ratio is at its highest point in human development.

Hence, at birth a newborn's head is approximately 25% of its total body height.