Where “ideal weight” comes from
The idea of an “ideal body weight” sounds scientific and precise, but its origins are surprisingly practical. The most famous formula was created in 1974 by Dr. B.J. Devine — not to tell people how much to weigh, but to help clinicians calculate medication doses. Many drugs are dosed by body size, and using actual weight can over-dose people who carry extra fat, since fat tissue doesn’t absorb most drugs the way lean tissue does. Devine needed a quick, height-based estimate of lean body size, and his formula stuck.
That history matters because it explains a lot of confusion. Ideal-weight formulas were never meant to be a personal goal — they’re rough estimates of a typical lean weight for a given height. The Ideal Weight Calculator shows four of them side by side precisely so you see a range rather than a single, misleadingly exact number.
The four classic formulas
All four formulas share the same shape. They define a base weight for someone five feet tall, then add a fixed amount for every inch above that height (and subtract for every inch below). They differ only in the numbers.
Devine (1974)
For men, Devine uses 50 kg plus 2.3 kg per inch over five feet; for women, 45.5 kg plus 2.3 kg per inch. It’s the most widely used formula, especially in medicine, and it’s the reference point the others were measured against.
Robinson (1983)
Robinson refined Devine using a larger dataset. Men start at 52 kg and gain 1.9 kg per inch; women start at 49 kg and gain 1.7 kg per inch. Robinson tends to give slightly lower numbers than Devine for taller people because the per-inch increment is smaller.
Miller (1983)
Miller also adjusted the coefficients: 56.2 kg for men plus 1.41 kg per inch, and 53.1 kg for women plus 1.36 kg per inch. Miller’s higher base but smaller per-inch slope means it produces a flatter range across heights.
Hamwi (1964)
The oldest of the four, Hamwi was designed as a fast bedside estimate. Men: 48 kg plus 2.7 kg per inch. Women: 45.5 kg plus 2.2 kg per inch. Its large per-inch increment makes it the most sensitive to height — it spreads out the most for very tall or very short people.
Because the coefficients differ, the four formulas can disagree by several kilograms for the same person. That spread isn’t a bug; it’s an honest reflection of how uncertain the whole concept is. Enter your height once in the Ideal Weight Calculator and you’ll see all four at once, plus their average.
Why BMI gives a range instead
There’s a completely different way to think about healthy weight: Body Mass Index. Instead of estimating a single ideal weight, BMI defines a band of weights considered healthy for a given height — specifically, the weights that put your BMI between 18.5 and 24.9. For someone 1.75 m tall, that’s roughly 57 kg to 76 kg, a generous 19 kg window.
This is arguably more honest than a single ideal-weight figure, because it acknowledges that healthy bodies come in a range of sizes. The Ideal Weight Calculator shows this BMI band alongside the four formulas, and you’ll notice the formula results usually fall comfortably inside it. If you want to understand the bands and their limitations in depth, our BMI chart explainer walks through exactly what each category means and where BMI breaks down.
The big limitation: body composition
Every formula on this page shares one blind spot: they only know your height and sex. They have no idea whether you’re carrying 20 kg of muscle or 20 kg of fat. A 1.80 m rugby player and a 1.80 m office worker get the identical “ideal weight,” even though their healthy weights might differ by 15 kg or more.
This is why ideal weight should never be treated as a hard target. Muscle is denser than fat, so fit, muscular people routinely sit “above” their ideal weight and above a healthy BMI while being in excellent health. The reverse is also true: someone can hit their “ideal” number while carrying too little muscle and too much fat — so-called normal-weight obesity. Tools that estimate metabolism, like a BMR calculator, or that look at body composition give a fuller picture than weight alone.
How to actually use these numbers
So what’s the point, if the numbers are this fuzzy? A few genuinely useful things:
- A sanity check. If your weight is wildly outside both the formula estimates and the BMI band, that’s worth a conversation with a doctor — in either direction.
- A starting band, not a target. Use the spread of the four formulas as a reasonable range to aim within, then adjust for your build and activity.
- Context for medical settings. Understanding that clinicians use ideal weight for drug dosing demystifies why a nurse might ask your height.
- A reminder that one number lies. Seeing four formulas disagree is a healthy antidote to the myth of a single perfect weight.
Informational only — not medical advice
This guide and the Ideal Weight Calculator are for general information. They are not medical advice and can’t account for your muscle mass, frame, age, or health conditions. Before setting a weight goal or making significant changes to your diet or exercise, talk to a doctor or registered dietitian who can look at the whole picture — not just a formula based on your height.
A worked example
It helps to see the numbers move. Take a man who is 1.78 m tall — about 70 inches, or 10 inches over five feet. Devine gives 50 + 2.3 × 10 = 73 kg. Robinson gives 52 + 1.9 × 10 = 71 kg. Miller gives 56.2 + 1.41 × 10 ≈ 70.3 kg. Hamwi gives 48 + 2.7 × 10 = 75 kg. The four answers span almost five kilograms — from about 70 to 75 kg — averaging roughly 72 kg. Meanwhile the healthy BMI band for 1.78 m runs from about 58.6 kg (BMI 18.5) to 78.9 kg (BMI 24.9). Every formula sits comfortably inside that band, toward its middle.
Now do the same for a woman of the same height. Devine: 45.5 + 2.3 × 10 = 68.5 kg. Robinson: 49 + 1.7 × 10 = 66 kg. Miller: 53.1 + 1.36 × 10 ≈ 66.7 kg. Hamwi: 45.5 + 2.2 × 10 = 67.5 kg. The estimates cluster around 67 kg — a few kilograms below the male figures at identical height, reflecting the sex-specific coefficients. The point of the exercise isn’t to pick a winner; it’s to internalise that the “right” answer is a band several kilograms wide, and that’s exactly what the Ideal Weight Calculator shows you in one view.
Height matters more than you’d think
Because every formula adds a fixed amount per inch, small differences in measured height shift the result noticeably — an inch can move the estimate by roughly 1.4 to 2.7 kg depending on the formula. That’s a good reason to measure height accurately (shoes off, standing tall, first thing in the day) rather than guessing, and another reason to treat the output as a range rather than a precise prescription.