Ideal weight calculator
Find your healthy weight range using four established medical formulas: Hamwi, Devine, Robinson, and Miller.
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About ideal weight formulas
These formulas were originally designed for clinical reference, especially for estimating medication dosing and other medical calculations, not for prescribing a single target body weight. They rely mostly on height and sex, and each formula produces a slightly different answer because there is no universally correct "ideal" weight for every person.
Using the average across several formulas gives a reasonable reference point, but it is still only a reference. Frame size, muscle mass, age, training history, and overall body composition all affect what a healthy weight looks like in practice. If you need a personalised target, clinical context matters more than any single formula.
The four formulas
Hamwi formula (1964)
Developed by Dr. G.J. Hamwi for estimating ideal body weight for insulin dosing in diabetic patients.
- Men: 48 kg for 5 feet of height, plus 2.7 kg for every inch above 5 feet
- Women: 45.5 kg for 5 feet, plus 2.2 kg for every inch above 5 feet
The Hamwi formula tends to produce lower ideal weight estimates than the others, particularly for taller individuals. It was designed for a specific clinical population and is now considered somewhat outdated for general use.
Devine formula (1974)
Developed by B.J. Devine, also originally for medication dosing — specifically for calculating gentamicin and other drug doses adjusted by lean body mass.
- Men: 50 kg + 2.3 kg per inch above 5 feet
- Women: 45.5 kg + 2.3 kg per inch above 5 feet
The Devine formula is widely used in clinical pharmacology and is still commonly referenced in medical dosing guidelines. It is also the basis for the "ideal body weight" used in many respiratory care calculations.
Robinson formula (1983)
A revision of the Devine formula by J.D. Robinson and colleagues, intended to better reflect population data available at the time.
- Men: 52 kg + 1.9 kg per inch above 5 feet
- Women: 49 kg + 1.7 kg per inch above 5 feet
The Robinson formula gives somewhat higher estimates than Devine and Hamwi, particularly for women, and is considered a closer fit to average healthy weights in Western populations.
Miller formula (1983)
Developed independently by D.R. Miller as another Devine revision.
- Men: 56.2 kg + 1.41 kg per inch above 5 feet
- Women: 53.1 kg + 1.36 kg per inch above 5 feet
The Miller formula produces the highest ideal weight estimates of the four, and is sometimes considered more appropriate for individuals with larger bone frames or higher muscle mass.
Ideal weight vs healthy weight range
The formulas above return a single number, but healthy weight is better understood as a range. The World Health Organization defines a healthy BMI as 18.5 to 24.9, which translates to a weight range that spans roughly 15–20 kg for most heights.
For example, a 5'9" (175 cm) man has a healthy BMI weight range of approximately 58 kg (128 lb) to 79 kg (174 lb) — a 21 kg span. Treating one number within that range as a single "ideal" oversimplifies a concept that is inherently individual.
Limitations of ideal weight formulas
They do not account for muscle mass. A trained athlete may weigh significantly more than their "ideal" weight while carrying less body fat than the formula implies. Conversely, someone at exactly the formula weight may have high body fat and low muscle mass — a condition sometimes called "normal weight obesity."
They were developed on limited populations. All four formulas were developed on predominantly white Western populations in the mid-20th century. They may not reflect healthy weight ranges for people of different ethnic backgrounds, who may have different body composition at the same height and weight.
They do not account for age. Older adults naturally carry somewhat more weight at a given height and frame size without adverse health consequences. Some research suggests the optimal BMI for longevity in older adults is in the 25–27 range — technically "overweight" by WHO standards.
They only use height and sex. Frame size, bone density, and natural body composition vary substantially between individuals of the same height. A large-framed person and a small-framed person of the same height can both be healthy at very different weights.
How to use the results
Treat the ideal weight output as a directional reference, not a target. The more useful exercise is to compare it against your current weight alongside other health indicators — body fat percentage, waist circumference, blood pressure, and metabolic markers — to get a fuller picture. A number sitting within the range suggested by multiple formulas and within the healthy BMI band is a reasonable general target; the exact formula value is not.
Frequently asked questions
Which ideal weight formula is the most accurate?
No single formula is universally most accurate — they were all developed for different clinical contexts, not as fitness targets. The Devine formula (1974) is the most widely used in medical dosing. For a general reference, the average of all four formulas gives a reasonable middle-ground estimate. Individual factors like muscle mass and frame size mean your healthy weight may differ significantly from any formula.
Is ideal weight the same as a healthy weight?
Not exactly. These formulas were designed for clinical pharmacology to improve drug dosing accuracy — not as health targets. A healthy weight is typically defined as a BMI between 18.5 and 24.9, which translates to a range of weights rather than a single number. The ideal weight from these formulas often falls near the middle of that healthy BMI range.
Why do male and female results differ?
Men and women have different typical body compositions at the same height. Women naturally carry a higher percentage of body fat, and these formulas apply different baseline values and multipliers for each sex to account for this difference. At the same height, the formulas generally produce a lower ideal weight for women than for men.
Do these formulas account for body frame size?
Most of these formulas do not directly account for frame size. The Hamwi formula does reference a medium frame and suggests adding or subtracting 10% for large or small frames respectively. In practice, people with a larger bone structure or more muscle mass may have a healthy weight that is higher than these formulas suggest.
Should I aim to reach my ideal weight?
These numbers are reference points, not targets you must hit. Many people are perfectly healthy at weights above or below what these formulas suggest. Focus on sustainable habits — regular exercise, adequate protein, good sleep — rather than reaching a specific number. If you are concerned about your weight, consult a healthcare professional for personalised guidance.
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