Ideal Weight Formulas Explained: Devine, Robinson, Miller, and Hamwi Compared

"Ideal weight" sounds like it should be a single, agreed-upon number, but in reality there are several different formulas in medical and fitness literature, each developed for a different purpose and each producing a slightly different result for the same person. Understanding where they come from helps explain why you might get several different "ideal weight" numbers depending on which calculator you use.

Why there isn't one universal formula

Most ideal weight formulas were developed decades ago for specific practical purposes — often to help clinicians estimate medication dosages — rather than as a definitive statement of what any individual should weigh. They use height and sex as inputs and produce a single number, without accounting for muscle mass, frame size, or body composition, which is why they should be read as rough reference points rather than precise targets.

The four most common formulas

Devine Formula (1974) — originally created for drug dosage calculations, this remains one of the most widely cited:

Robinson Formula (1983) — a refinement of Devine's approach with slightly adjusted constants:

Miller Formula (1983) — tends to produce slightly higher estimates than Robinson or Devine:

Hamwi Formula (1964) — one of the oldest, originally designed as a quick mental-math estimate for clinical use:

Where the formulas came from

The oldest widely known rule is the Broca index, proposed by the French physician Paul Broca in 1871, which says that your ideal weight in kilograms is your height in centimeters minus 100. In 1964 G.J. Hamwi published a formula for estimating ideal body weight for patients, and in 1974 B.J. Devine produced a similar formula that was intended to help estimate drug dosages. The Robinson and Miller formulas followed in 1983. These formulas were never designed to define a perfect weight for everyone. They were developed as quick clinical estimates, which is why they give slightly different answers.

The story of BMI

Body mass index goes back to the Belgian mathematician Adolphe Quetelet, who in the 1830s and 1840s studied average body proportions and found that weight scales roughly with the square of height in adults. The measure was called the Quetelet index until 1972, when the physiologist Ancel Keys and colleagues compared several indices and renamed it body mass index, arguing it was a practical way to describe weight in populations. Standard categories today put a healthy range at a BMI of 18.5 to 24.9. BMI was designed for studying groups, and it cannot tell muscle from fat.

Limits of any single number

• Muscular people can have a high BMI without excess fat.
• Older adults can have a normal BMI but low muscle mass and higher fat percentage.
• Body frame, ethnicity, age and sex all influence where a healthy weight sits.
• Where fat is stored matters. Abdominal fat is linked with higher health risk than fat on the hips and thighs.

Other useful checks

Waist circumference and waist-to-height ratio can add information. A commonly cited guideline from the UK's National Institute for Health and Care Excellence suggests keeping your waist measurement to less than half your height. Blood pressure, blood sugar, cholesterol and fitness level often say more about health than weight alone. Instead of aiming for a single number, think of a healthy range and track habits such as activity, sleep and food quality. The Ideal Weight Calculator, Healthy Weight Calculator and BMI Calculator on this site show how the formulas compare. This article is general information, not medical advice.

Why the results differ

All four formulas share the same basic structure — a base weight for 5 feet of height, plus an additional amount per inch above that — but the constants differ because each was calibrated against different reference populations and for different clinical goals. For a 5'10" man, the four formulas can produce ideal weight estimates that differ by 4–6 kg (roughly 9–13 lbs) from each other, which is a meaningful spread for something often treated as a single "ideal" number.

What these formulas leave out

None of these formulas account for frame size, muscle mass, or body composition — the same limitations that affect BMI. A muscular, athletic person will often weigh more than these formulas suggest without carrying excess fat, while someone with a naturally smaller frame might have a healthy weight below the formula's estimate. For that reason, these formulas are best used as one data point among several — alongside BMI, body fat percentage, and how you actually feel and function — rather than as a strict target to hit.

This calculator provides general informational estimates and is not a medical diagnosis. If you have concerns about your health or weight, consider speaking with a qualified healthcare professional.