The four classic formulas
Devine: 50 kg (men) or 45.5 kg (women) + 2.3 kg per inch over 5 feet. Originally built for drug-dose calculations, not health.
Robinson: 52 kg (men) / 49 kg (women) + 1.9 kg / 1.7 kg per inch over 5 ft. A tweak of Devine, slightly gentler.
Miller: 56.2 kg / 53.1 kg + 1.41 kg / 1.36 kg per inch over 5 ft.
Hamwi: 48 kg / 45.5 kg + 2.7 kg / 2.2 kg per inch over 5 ft. The most aggressive of the four.
Why modern practice uses BMI instead
All four formulas were derived from small clinical samples and target a single point, ignoring frame size, muscle, and healthy natural variation. They routinely under-target women and taller people.
The WHO and CDC now define a healthy weight as BMI 18.5–24.9. That's a range, not a number, and it's been validated on tens of millions of people worldwide.
If you want one number, take the mid-range of your BMI band and adjust for frame size — you'll land close to the classic formulas but with a defensible modern rationale.
