Robinson Formula for Ideal Body Weight

Robinson’s equation, published in 1983, is the second most-used ideal body weight formula in US pharmacy. In the form everyone runs it: men 52 kg plus 1.9 kg per inch above five feet; women 49 kg plus 1.7 kg per inch. The paper it comes from is titled Determination of ideal body weight for drug dosage calculations — the purpose is stated in the title.

The field takes centimeters, where the slopes are about 0.75 kg/cm for men and 0.67 for women.

Worked, in inches

A man of 5 ft 10 in is ten inches above the baseline: 52 + 1.9 × 10 = 71.0 kg = 157 lb. A woman of 5 ft 4 in is four inches above: 49 + 1.7 × 4 = 55.8 kg = 123 lb.

The two versions of the coefficients

Worth knowing before you compare calculators. The 1983 paper printed 51.65 kg + 1.85 kg/inch for men and 48.67 kg + 1.65 kg/inch for women — the raw output of its regression — and those exact figures are what the StatPearls pharmacy calculations chapter still carries. What circulated afterwards, including in the 2016 American Journal of Clinical Nutrition review of these equations and in the calculator above, is the tidied 52 / 1.9 and 49 / 1.7.

The gap is small and one-directional: the rounded version runs about a pound high at 5 ft 3 in and two pounds high at 5 ft 11 in. For dosing it is irrelevant. For a page claiming to state the formula, the distinction is worth the sentence.

Robinson against Devine, and where they cross

Robinson starts higher at five feet and climbs more slowly than Devine, so the two lines intersect. For men that happens at exactly 65 inches:

Height	Devine, men	Robinson, men	Devine, women	Robinson, women
5 ft 2 in	120 lb	123 lb	110 lb	116 lb
5 ft 6 in	141 lb	140 lb	131 lb	131 lb
5 ft 10 in	161 lb	157 lb	151 lb	146 lb
6 ft 2 in	181 lb	173 lb	171 lb	160 lb

So the common claim that Robinson simply returns lower numbers is only true above 5 ft 5 in. Below that it is the higher of the two, and at six foot two the two equations disagree by eight pounds for a man and eleven for a woman.

Why there are four of these at all

Hamwi in 1964, Devine in 1974, Robinson and Miller both in 1983 — four equations, one purpose. They are close cousins because they were fitted to the same source: Metropolitan Life insurance height–weight tables, which recorded what policyholders weighed, not what kept them healthy. Each author re-ran the regression and published a slightly different straight line.

Peterson and colleagues showed in 2016 that all of them share a structural fault, underestimating weight at short heights and overestimating it at tall ones, because a straight line cannot track a ratio that squares height. Their replacement returns body weight at any target BMI instead of one ideal number.

Not a weight goal

Robinson’s output has no term for what you weigh now, how old you are or how much of you is muscle. US agencies do not publish an ideal weight; the NHLBI publishes a healthy range of BMI 18.5 to 24.9, which at 5 ft 7 in is 119 to 159 lb. For that band, use the ideal weight calculator or the height-specific page for 5 ft 7 in.

This content is informational and does not replace evaluation by a health professional.