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How the Devine Formula Estimates Ideal Body Weight

Ideal body weight calculators almost always run on a formula from 1974 that was never designed to define a healthy weight in the first place.

Men: 50 kg + 2.3 kg per inch over 5 feet

The Devine formula starts at 50 kg for a man at exactly 5 feet (152.4 cm) tall, then adds 2.3 kg for every inch of height above that. A man who is 5'10" (10 inches over 5 feet) works out to 50 + (2.3 x 10) = 73 kg.

Women: 45.5 kg + 2.3 kg per inch over 5 feet

The same structure applies to women with a lower starting point, 45.5 kg at 5 feet, plus the same 2.3 kg per additional inch. The per-inch rate is identical between sexes; only the baseline differs.

It was built for drug dosing, not fitness goals

B.J. Devine published the formula in 1974 specifically to help clinicians estimate dosing for medications like aminoglycoside antibiotics, where dosing by actual body weight can overshoot for larger patients. It was never intended as a personal health or aesthetic target.

Under 5 feet, the formula extrapolates downward

For someone shorter than 5 feet, the same per-inch rate is typically applied in reverse, subtracting from the baseline. Results get less reliable the further height strays from the adult population the formula was built around.

Other IBW formulas give different numbers

Robinson (1983), Miller (1983), and Hamwi (1964) are competing ideal-weight formulas with slightly different constants. Plugging the same height into each one produces a range of "ideal" weights, not a single agreed-upon number.

Why four formulas never agree

Devine, Robinson, Miller, and Hamwi were each derived from different reference populations and rounding choices decades apart, so none of them is more "correct" than the others in an absolute sense. Clinical dosing calculators sometimes average two or more of them specifically because no single formula is treated as definitive.

What the formula cannot see

Because ideal body weight formulas use only height and sex, they cannot account for frame size, muscle mass, or fat distribution. A muscular, large-framed adult and a small-framed adult of the same height and sex get the identical "ideal" number, even though a healthy weight for each of them may look quite different in practice.

Frequently Asked Questions

Is being above my Devine ideal weight automatically unhealthy?

No. The formula is a rough population-level reference point, most heavily used in clinical dosing contexts, not a personal health verdict. Frame size, muscle mass, age, and overall health context matter more than matching a single formula's output exactly.

Why doesn't the formula account for body frame or muscle mass?

Because it was designed for quick clinical estimation using only the two data points doctors would have on hand instantly, height and sex, not for a comprehensive personal health assessment. Formulas that also weigh frame size exist but are used far less often in practice.