Is There Really an 'Ideal Weight'? The Formulas and Their Flaws

The number that doesn't exist (quite)

"What's my ideal weight?" feels like it should have one clean answer. It doesn't — and the reason is revealing. Several well-known formulas claim to tell you, and they disagree with each other, sometimes by several kilograms for the same person. That disagreement isn't a bug to be fixed; it's a signal that "ideal weight" is a far softer idea than it sounds. Knowing where these formulas came from, and what they can't see, turns a potentially anxiety-inducing number into a useful but modest guide.

Where the formulas came from

The familiar ideal-weight formulas mostly date to the mid-20th century, and — like BMI — several were built for purposes that had little to do with general health or fitness:

• Devine (1974) — the most widely used, originally devised to help calculate medication dosages, where an estimate of lean body size matters. It was never meant as a lifestyle goal.
• Robinson (1983) and Miller (1983) — refinements of Devine's approach using different data.
• Hamwi (1964) — an earlier rule of thumb from clinical practice.

Each follows the same shape: a base weight at 5 feet (152 cm) of height, plus a fixed amount of weight per inch above that. The specific base and per-inch figures differ between formulas because they came from different datasets and goals — which is exactly why they produce different answers.

Why they disagree

Run your height through all four and you'll get a spread of several kilograms. That's not error so much as honesty: each formula encodes slightly different assumptions about how weight "should" scale with height, drawn from different populations and eras (some rooted in old life-insurance tables). None is objectively "the right one."

The sensible response isn't to pick a favourite and treat it as truth. It's to see the range they collectively suggest, and to cross-check it against the healthy weight range implied by BMI (a BMI of 18.5–24.9 for your height). That's precisely what the Ideal Weight Calculator does — showing all four formulas, their average, and the BMI-based healthy band side by side, so you see a sensible span rather than a false precision.

The blind spot they all share

Every one of these formulas has the same fundamental limitation as BMI: they use only height and sex. Nothing about your muscle mass, bone structure, or body composition enters the calculation.

That means they can't distinguish a muscular, broad-framed person from a slight one of identical height — yet those two people have genuinely different healthy weights. A muscular athlete will often sit well above their formula-derived "ideal" while being lean and perfectly healthy, because muscle is dense. An older or sedentary person could hit the "ideal" number while carrying excess fat and too little muscle. A single weight target, however it's derived, simply can't capture this — which is the core reason "ideal weight" deserves scepticism as a personal goal.

A range, not a target

So what should you actually aim for? The more useful framing replaces the single number with a healthy range plus context:

• A healthy weight range for your height (the BMI band is a reasonable guide), rather than one magic figure.
• Body fat percentage — what your weight is made of matters more than the weight itself.
• Waist circumference — a simple, powerful indicator of the abdominal fat most linked to health risk.
• Fitness and function — how you move, perform, and feel.

Weight is one signal among several, and it's a laggy, noisy one (it swings with hydration, food, and muscle). Chasing a precise formula-derived "ideal" tends to cause more anxiety than insight. Aiming for a sensible range while improving body composition and fitness is both healthier and more achievable — and it sidesteps the fact that the formulas can't agree on the target anyway.

Seeing your range

Enter your height into the Ideal Weight Calculator to compare the formulas and the healthy BMI range, then add context with the Body Fat Calculator and BMI Calculator.

Sources

1. Devine, B. J. Original ideal body weight formula for drug dosing (1974).
2. Robinson, J. D. et al. and Miller, D. R. et al. Ideal body weight equations (1983).
3. Pai, M. P. & Paloucek, F. P. "The Origin of the 'Ideal' Body Weight Equations," Annals of Pharmacotherapy (2000).

---

This article is for general informational and educational purposes only and is not medical advice. A healthy weight is individual; consult a healthcare professional for guidance tailored to you.