❤️ Health
What Is My Ideal Weight? The Formulas Explained
There's no single ideal weight. Here's what the Robinson, Miller, Devine and Hamwi formulas say, how they compare to a healthy BMI range, and how to read the numbers sensibly.
Updated 28 September 2026 · 2 min read
Ask what your 'ideal weight' is and you'll get several different answers, because there isn't one number — there are competing formulas, each built for a slightly different purpose. The honest takeaway is that ideal weight is a range, not a target, and it depends on far more than height alone.
The four classic formulas
Most 'ideal body weight' estimates trace back to four formulas developed for clinical use, largely to help dose medication by body size. They all start from a baseline weight at 5 feet (152 cm) and add a fixed amount per inch above that:
- Devine (1974) — the most widely used in medicine. For men: 50 kg + 2.3 kg per inch over 5 ft.
- Robinson (1983) — a refinement of Devine that tends to give slightly lower figures.
- Miller (1983) — similar vintage, with a gentler increase per inch.
- Hamwi (1964) — the oldest, originally a quick bedside estimate, usually the highest of the four.
The ideal weight calculator runs all four at once for your height and sex, so you see the spread rather than a single false-precision number. Women's versions of each formula use a lower baseline, reflecting differences in average build.
Why a BMI range matters more
Those formulas predate modern population data, so the calculator also shows the weight range that corresponds to a healthy BMI (18.5 to 24.9) for your height. This is usually the more useful figure, because it's a band, not a point — and being anywhere inside it is fine.
That's a spread of nearly 20 kg for the same height — which tells you just how loose the idea of a single 'ideal' really is. If you want to understand the number behind the range, our guide to what BMI actually tells you breaks it down.
What the formulas leave out
None of these methods know anything about your body composition, and that's their biggest blind spot:
- Muscle weighs more than fat by volume. A lean, muscular person can sit 'above' their ideal weight while carrying very little fat.
- Frame size varies. Bone structure and build differ between people of identical height.
- Age and sex shift the picture. Body composition changes over a lifetime in ways a height-only formula can't capture.
For a fuller picture, pair the ideal-weight estimate with a look at body fat percentage, which speaks to composition rather than just the number on the scale.
How to use the numbers
Treat the formulas as a ballpark, and the healthy-BMI range as a sensible zone to aim for. If you're comfortably inside the range, feel well and are active, chasing a specific formula's figure gains you nothing. If you're well outside it and want to change that, focus on habits — food, movement, sleep — rather than a target weight, and talk to a GP if you have health concerns.
Frequently asked questions
- Which ideal weight formula should I trust?
- None of them exclusively. They were designed for medication dosing, not as personal goals. Use the healthy-BMI weight range as your main reference and treat the four formulas as a rough cross-check that gives you a spread rather than a single number.
- Why do the four formulas give different answers?
- They were built in different decades from different data and assumptions, so they disagree — often by several kilograms. That disagreement is the point: it shows 'ideal weight' is inherently fuzzy, not a precise figure.
- Is being outside my 'ideal weight' unhealthy?
- Not necessarily. The formulas ignore muscle, frame and composition, so athletes in particular can read as over their ideal while being very healthy. A healthy BMI range, activity level and how you feel matter more than any single formula.