Why 4 different formulas
There is no single, definitive ideal weight formula. Throughout the 20th century, various researchers proposed their own equations based on distinct population samples and criteria. Displaying all four together, rather than picking just one, provides a more honest picture: ideal weight is a reference range rather than an exact number.
Ideal weight vs. BMI: what is the difference
The BMI uses your current weight and height to classify your weight into categories (underweight, normal weight, overweight, obesity). Ideal weight formulas work in reverse: using only height and sex, they estimate a target reference weight without knowing your current weight. They are complementary tools, not replacements for each other.
Origin of the formulas
These equations were originally developed for clinical use, particularly for calculating proper drug dosages based on body weight, rather than serving as general weight goals for the public. The Devine formula, for instance, is still widely used in hospital settings today for this purpose.