Enter your height, sex and frame size and this calculator returns your ideal body weight from all five recognised formulas at once — Devine, Robinson, Miller, Hamwi and the modern Peterson equation — rather than picking one and hiding the disagreement. Alongside them it shows the WHO healthy BMI weight range for your height, which is usually the more useful target, and will compare your current weight against both if you enter it. For a measure that distinguishes muscle from fat, try the body fat calculator, or the BMI calculator for the standard screening figure.
Ideal Weight Calculator
Five ideal-weight formulas at once, plus the healthy BMI range they should be read against.
Estimate frame from your wrist: wrap thumb and middle finger around it. Overlapping means small, just touching means medium, not meeting means large.
Ideal weight (average of five formulas)
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Healthy BMI range—
Frame adjustment—
Each formula
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Where "ideal weight" comes from
Ideal body weight formulas were not designed for aesthetics or fitness. Most were built in the 1960s and 1970s for clinical use — chiefly to calculate drug dosages, which depend on lean mass rather than total mass, and to set nutritional targets. That origin explains their character: they take height and sex as the only inputs and return a single number, ignoring muscle mass, bone density, age and body composition entirely.
The five formulas
Hamwi (1964) is the oldest and gives the most generous figures for tall people. Devine (1974) became the default in clinical pharmacology and is still the most widely cited — 50 kg plus 2.3 kg for every inch over five feet for men, 45.5 kg plus 2.3 kg per inch for women. Robinson (1983) and Miller (1983) were both revisions of Devine intended to improve accuracy at the extremes; Miller returns the lowest numbers for tall people, Robinson sits in between.
Peterson (2016) is the modern outlier and the most defensible of the group. Rather than anchoring to five feet and adding a fixed increment per inch, it derives ideal weight from a target BMI of 22 with a proper height relationship: 2.2 × BMI + 3.5 × BMI × (height in metres − 1.5). Because it is BMI-based it stays sensible at heights where the older linear formulas drift, and unlike them it does not use different constants for men and women.
Why they disagree
At average heights the five formulas land within a few kilograms of each other. At the extremes they diverge sharply — for someone 6'6" the spread can exceed 10 kg — because the older ones extrapolate a fixed per-inch increment far beyond the height range they were fitted to. This is exactly why showing all five side by side is more useful than picking one: the spread is itself the honest answer about how precise the concept can be.
The healthy BMI range is the better target
A range beats a single number. The WHO healthy BMI band of 18.5 to 24.9 converts to a weight range for your height that is typically 15–20 kg wide, and any weight inside it is compatible with good health. Most people are better served aiming somewhere in that band than chasing a specific formula output to the decimal.
The limits worth knowing
None of these formulas can tell muscle from fat. A trained athlete will routinely sit above their "ideal" weight while carrying less fat than someone at it, and an inactive person can hit the number exactly while carrying too much fat and too little muscle — the pattern sometimes called normal-weight obesity. They are also poorly validated for people under 18, during pregnancy, for the elderly, and for anyone with limb loss or significant fluid retention. Body composition tells you far more: see the body fat calculator for a measure that separates the two.
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Frequently asked questions
Which ideal weight formula is most accurate?
Peterson (2016) is the best-founded of the five because it derives from a target BMI with a proper height relationship rather than adding a fixed amount per inch above five feet. Devine remains the most widely used clinically, largely for continuity with existing drug-dosing protocols.
Why do the five formulas give different answers?
They were fitted to different populations for different purposes, and the older four all use a linear 'base weight plus so much per inch over 5 feet' structure that drifts at unusual heights. Near average height they agree closely; at the extremes the spread widens considerably.
Should I actually aim for my ideal weight?
Treat it as a reference point, not a target. The healthy BMI range for your height is a better goal because it is a range, and body composition matters more than either — a muscular person above their ideal weight can be healthier than a sedentary person at it.
Does ideal weight change with age?
The formulas do not adjust for age, but the evidence suggests slightly higher body weight is protective in older adults. Muscle mass also declines with age, so holding the same weight at 60 as at 30 usually means carrying more fat and less muscle.
How do I work out my frame size?
Wrap your thumb and middle finger around the opposite wrist. If they overlap you have a small frame, if they just touch it is medium, and if they do not meet it is large. Small frames adjust down about 10% and large frames up about 10%.
Does this apply to children or during pregnancy?
No. These formulas were developed for non-pregnant adults. Children should be assessed against age-and-sex growth percentiles, and pregnancy weight targets depend on pre-pregnancy BMI — see a pregnancy weight gain calculator or your midwife for that.