A new body mass index, termed Consistent Body Mass Index CBMI=\(\:\sqrt{m/{h}^{3}}\), is developed from first principles. Customarily used Body Mass Index (BMI\(\:=m/{h}^{2}\)) or its variant Tri-ponderal Mass Index (TMI\(\:=m/{h}^{3}\)) or other measures serving to the purpose of classifying the anthropometric status of a person have repeatedly been demonstrated to be unsatisfactory in various aspects. A new index inclusive of all ages, body sizes, and sexes is therefore needed. A non-dimensional hence scalable index CBMI, which correlates well with waist-to-height ratio, \(\:w/h\), is developed from fundamental relations. Correlation levels of CBMI and TMI against waist-to-height ratio \(\:w/h\) are compared for measurements comprising participants ranging from 1-day-old to 75-year-old male and female infants, children, and adults. Waist-to-height ratio \(\:w/h\), which correlates well, \(\:r=0.84\), with CBMI is a reliable measure of the anthropometric status of a person. New criteria and relevant charts, based on \(\:w/h\) and CBMI, are established for classifying anthropometric status levels. CBMI can also be used as an estimator for ideal body weight for a definite CBMI value and a given height \(\:h\) from \(\:m={\left(\text{C}\text{B}\text{M}\text{I}\right)}^{2}{h}^{3}\).
