Ideal Weight (Robinson)

About Ideal Weight (Robinson)

The Robinson formula, published by J. D. Robinson and colleagues in 1983 in the Annals of Internal Medicine, is a refinement of the earlier Devine ideal body weight formula. Robinson re-examined the relationship between height and desirable weight using the 1959 and 1983 Metropolitan Life Insurance Company height and weight tables and the Build and Blood Pressure Study data. By regressing the midpoint of the medium-frame desirable weight ranges on height, Robinson derived new coefficients that he argued better reflected actuarially desirable weights than Devine's empirically chosen values.

How the formula works

The Robinson formula uses the same structure as Devine: a base weight at 5 feet (60 inches) plus a per-inch increment above that height. For men: IBW = 52 + 1.9 x (height in inches - 60). For women: IBW = 49 + 1.7 x (height in inches - 60). Compared with Devine, Robinson's base values are slightly higher (52 vs 50 kg for men; 49 vs 45.5 kg for women) and the per-inch increments are slightly lower (1.9 vs 2.3 kg for men; 1.7 vs 2.3 kg for women). The net effect is that Robinson predicts slightly higher weights at 5 feet and slightly lower weights at tall statures compared with Devine, producing a flatter slope that reflects the actuarial data.

Evidence and comparison with Devine

Robinson derived his formula from formal linear regression against the midpoint of medium-frame desirable weight ranges in the Metropolitan Life tables, which gives it a stronger empirical basis than Devine's formula (which was based on clinical judgment). The two formulas agree closely for adults of average height but diverge at the extremes: at 6 feet (183 cm), Robinson predicts about 76.6 kg for men, while Devine predicts 77.3 kg; at 5 feet, Robinson predicts 52 kg versus Devine's 50 kg. A 2007 comparison by Shah and colleagues found that the four major IBW formulas (Devine, Robinson, Miller, Hamwi) generally agree within 2 to 4 kg for average-height adults.

Interpretation

The Robinson formula gives a single ideal weight target that corresponds approximately to the middle of the healthy BMI range (BMI 22 to 23). As with other IBW formulas, a plus or minus 10 percent adjustment for frame size is commonly applied. The Robinson target is slightly higher than Devine for short adults and slightly lower for tall adults, which some clinicians prefer because it better matches actuarial mortality data.

When to use it

The Robinson formula is used as an alternative to Devine for ideal weight estimation, particularly when the user wants a formula derived from formal regression rather than clinical empiricism. It is used in nutrition assessment, weight-management counseling, and as a reference for healthy weight targets. Because the differences between Robinson and Devine are small for most adults, the choice between them is often a matter of institutional preference.

Limitations

Like all IBW formulas, Robinson's equation does not account for frame size, age, body composition, or muscle mass. It was derived from insurance actuarial data, which overrepresents middle-class white adults from the mid-20th century and may not generalize to modern multiethnic populations. The formula gives a single point estimate rather than a range, and the linear per-inch assumption breaks down at the extremes of stature. It should not be used for children, pregnant women, athletes, or the very elderly without adjustment. For most contemporary applications, BMI-based ideal weight (weight at BMI 22) or body-composition-based targets are preferred, but the Robinson formula remains a useful reference and is built into many nutrition and pharmacy calculators.