The Corpulence Index (CI) or Ponderal Index (PI) is a measure of leanness of a person calculated as a relationship between mass and height. It was first proposed in 1921 as the "Corpulence Index" by Rohrer and hence also known as Rohrer's Index. It is similar to the body mass index, but the mass is normalized with the third power of body height rather than the second power.

For a baby, it is calculated as

with in kg (kilograms) and in m (meters), giving a measure with the same dimensions as density. The corpulence index yields valid results even for very short and very tall persons. Because of this property, it is most commonly used in pediatrics. The normal values for infants are about twice as high as for adults, which is the result of their relatively short legs. It does not need to be adjusted for age after adolescence.