Which ideal weight formula is most accurate?

None of the four formulas was originally designed to define a 'healthy' weight for the general population — they were developed for drug dosing in clinical settings. The Devine formula is the most widely cited in pharmacology. For general health, BMI and body composition measurements are more relevant.

What if my actual weight is above my ideal weight?

These formulas provide a rough reference range, not a personal health target. A person can be at a higher weight and still be metabolically healthy depending on muscle mass, genetics, and lifestyle. Consult a healthcare provider for individualised guidance.

Why do the four formulas give different results?

Each formula was derived from different patient populations and measurement methods in different decades. The differences are typically 2–5 kg, reflecting measurement uncertainty rather than meaningful clinical differences.

Ideal Weight Calculator

The concept of “ideal body weight” (IBW) has been used in medicine and pharmacology for over 60 years. Rather than returning a single number, our calculator gives you results from four different validated formulas, giving you a realistic range and helping you understand how the formulas differ.

The Four Formulas

Devine (1974) — Most Widely Used

Developed by B.J. Devine for calculating gentamicin antibiotic dosing, this formula became the gold standard in clinical pharmacology:

Male: IBW = 50 + 2.3 × (height in inches − 60)
Female: IBW = 45.5 + 2.3 × (height in inches − 60)

Robinson (1983)

An update to Devine designed to improve accuracy for a broader population:

Male: IBW = 52 + 1.9 × (height in inches − 60)
Female: IBW = 49 + 1.7 × (height in inches − 60)

Miller (1983)

Another 1983 revision, tends to give slightly higher estimates:

Male: IBW = 56.2 + 1.41 × (height in inches − 60)
Female: IBW = 53.1 + 1.36 × (height in inches − 60)

Hamwi (1964) — Oldest Formula

Originally published by G.J. Hamwi as a dietary guideline:

Male: IBW = 48 + 2.7 × (height in inches − 60)
Female: IBW = 45.5 + 2.2 × (height in inches − 60)

All formulas use inches above 5 feet (152.4 cm) as the base calculation unit. Heights at or below 5 feet return the base constant.

Worked Example

Male, 175 cm (5 ft 9 in):

Inches over 5 ft = 175/2.54 − 60 ≈ 8.9 inches
Devine: 50 + 2.3 × 8.9 = 70.5 kg
Robinson: 52 + 1.9 × 8.9 = 68.9 kg
Miller: 56.2 + 1.41 × 8.9 = 68.7 kg
Hamwi: 48 + 2.7 × 8.9 = 72.0 kg

The range (68.7–72.0 kg) gives a clinically reasonable spread. A weight anywhere in this range, or moderately above or below, is not inherently problematic.

Important Limitations

These formulas were not designed as health targets. They were developed in hospital settings for calculating initial drug doses (particularly aminoglycoside antibiotics like gentamicin) that are distributed in lean body mass. The “ideal” in “ideal body weight” is a pharmacological term, not a beauty or fitness standard.

Body composition matters more than weight. A muscular person may be well above their IBW and be in excellent health. Conversely, someone at their IBW with high body fat may face metabolic risks. BMI, body fat percentage, and waist-to-height ratio are more comprehensive health indicators.

Ethnicity and age adjustments. Research suggests different populations may have different optimal weight-to-height ratios. Older adults often maintain better health at slightly higher weights due to muscle and bone reserve.

Frequently Asked Questions

How accurate are these formulas? For their intended purpose (drug dosing), these formulas are clinically validated. For general health guidance, they are rough reference points only. Individual variation in bone density, muscle mass, and metabolic health means the “ideal” weight can vary significantly between people of identical height.

Should I aim for my ideal body weight? Not necessarily. These formulas are starting points for conversation with a healthcare provider. A sustainable, healthy weight for you depends on your body composition, genetics, fitness level, and medical history.

Why are male IBW values higher than female values at the same height? Men typically have larger bone frames and more muscle mass at the same height, justifying higher absolute weight targets in the original drug-dosing context.