Your "ideal weight" was invented to calculate a drug dose

There is something quietly misleading about the phrase "ideal weight." It suggests a number you are supposed to reach, as if health had a single correct answer printed somewhere. The truth is more mundane: the most common "ideal body weight" formula was created in 1974 by a researcher named B. J. Devine for a very specific purpose — estimating drug dosages, particularly for gentamicin, an antibiotic. It was a pharmacy tool, not a wellness goal.

A formula built for the pharmacy, not the mirror

The Devine formula is simple: start at 50 kg for men (45.5 for women) and add 2.3 kg for every inch above five feet. It produces a single number, which made it useful for clinicians who needed a quick, standardized weight estimate when prescribing weight-based medications. "Useful for dosing" is a long way from "this is what you should weigh."

Other formulas exist — Robinson, Miller, Hamwi — and they produce slightly different numbers for the same person. If there were one true ideal weight, they would agree. The fact that they do not is the clearest evidence that "ideal weight" is a convention, not a fact.

What a single number leaves out

A healthy weight depends on body composition, not just height. Two people of the same height and weight can differ dramatically in muscle, bone density, and fat distribution. The Devine formula sees none of that — it sees only height. An athlete carrying significant muscle will read as "over" an ideal-weight estimate while being metabolically healthy, while the same reading for someone else can mean something entirely different.

Why ranges beat point estimates

Even when a weight goal is useful, a range is almost always more honest than a point. A common convention treats the healthy range as roughly plus or minus 10% around an ideal-weight estimate. The real takeaway is not "you must weigh exactly this," but "here is a ballpark to help frame a conversation about what a reasonable target might look like for you."

If a number like this is going to be useful at all, it is as context — one data point among BMI, waist measurement, activity, and how you actually feel. A number that was invented to dose an antibiotic was never designed to be the last word on your body.

"Ideal weight" is a general reference value. A healthy weight is individual — discuss appropriate goals with a healthcare professional.