What Is My Ideal Weight? Comparing 5 Scientific Formulas

A brief history of ideal body weight

The concept of an "ideal" body weight has been a cornerstone of clinical medicine for over half a century. What many people do not realize is that the most commonly used formulas were never designed as health benchmarks for the general public. They were created by pharmacists and physicians who needed a quick way to dose medications — particularly aminoglycoside antibiotics and anesthetic agents — in patients whose actual weight included varying amounts of body fat that does not absorb drugs the same way lean tissue does.

Over the decades these equations migrated from drug dosing charts into nutrition textbooks, fitness apps, and insurance tables. Today they remain the most widely referenced standards for ideal weight, even though their original purpose was far more specific. Understanding this history helps you interpret the numbers with appropriate context rather than treating any single formula as an absolute truth.

The four clinical formulas explained

Devine formula (1974)

Dr. B.J. Devine published this equation in 1974 as part of a paper on gentamicin dosing. For men it estimates ideal weight as 50 kg plus 2.3 kg for each inch above 5 feet; for women, 45.5 kg plus 2.3 kg per extra inch. Despite being created for a single antibiotic, the Devine formula became the default in medical calculators worldwide and is still embedded in ventilator tidal volume settings, drug dosing software, and BMI-based clinical protocols. Its simplicity is both its strength and its weakness: it is easy to memorize and apply, but it systematically underestimates healthy weight for taller individuals and overestimates it for shorter people.

Robinson formula (1983)

Robinson and colleagues revisited the Devine equation in 1983 using actuarial data from the Metropolitan Life Insurance tables. Their refined coefficients — 52 kg base for men (1.9 kg per inch) and 49 kg for women (1.7 kg per inch) — produce slightly different estimates that tend to be a few kilograms lower for tall men and a few kilograms higher for shorter women compared to Devine. The Robinson formula is particularly common in pharmacy practice and is referenced in many hospital formularies.

Miller formula (1983)

Published in the same year as Robinson, the Miller formula uses higher base values (56.2 kg for men, 53.1 kg for women) but lower per-inch increments (1.41 and 1.36 respectively). This produces estimates that are notably higher at 5 feet but converge with the other formulas around 5 foot 10 inches. Miller is less commonly used in clinical practice but provides a useful upper bound when comparing formula ranges.

Hamwi formula (1964)

George Hamwi developed his formula a decade before Devine, originally for dietary planning in diabetes management. Men start at 48 kg with 2.7 kg per extra inch; women at 45.4 kg with 2.2 kg per inch. Of all four formulas, Hamwi produces the highest estimates for tall individuals because of its steeper per-inch coefficient for men. Despite its age, it remains widely used in dietetics education and diabetes care planning.

The WHO BMI approach

Rather than prescribing a single ideal number, the World Health Organization defines a healthy weight range using Body Mass Index (BMI). A BMI between 18.5 and 24.9 kg/m squared is considered healthy for most adults. This translates into a range of acceptable weights for any given height — for example, a person who is 170 cm tall has a healthy weight range of approximately 53.5 to 72.0 kg.

The WHO approach has the advantage of acknowledging that healthy body weight is a range, not a point. It is also the basis for most epidemiological research linking weight to health outcomes. However, like the clinical formulas, BMI does not distinguish between fat mass and lean mass, which limits its accuracy for athletes, elderly individuals, and certain ethnic groups.

When clinicians actually use these formulas

In modern clinical practice, ideal body weight formulas are used primarily for drug dosing (especially for aminoglycosides, chemotherapy agents, and mechanical ventilation settings), for setting initial calorie targets in critically ill patients, and as a quick reference in primary care. Anesthesiologists calculate tidal volumes based on ideal rather than actual weight to protect the lungs. Pharmacists use adjusted body weight (a blend of ideal and actual) for obese patients receiving weight-based medications.

Outside of these specific clinical contexts, most evidence-based guidelines recommend using BMI ranges, waist circumference, or body composition analysis rather than point-estimate formulas to assess whether someone is at a healthy weight.

Key limitations you should know

Beyond the number: body composition matters more

Research increasingly shows that body composition — the ratio of fat mass to lean mass — is a far better predictor of metabolic health than weight alone. Two people at identical heights and weights can have dramatically different health profiles depending on how much of their weight is muscle versus adipose tissue. A 2017 review in Advances in Nutrition concluded that body composition measures are more important predictors of cardiometabolic risk than BMI or ideal weight calculations.

Methods like DEXA scans, bioelectrical impedance analysis, skinfold measurements, and even simple waist-to-hip ratio measurements provide far more actionable information than any height-based formula. If you are serious about understanding your health status, consider these tools as complements to — not replacements for — weight-based estimates.

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