The concept of an "ideal body weight" sounds intuitive — yet fewer than one in ten people know where the number comes from, or that clinicians routinely use four completely different formulas that can produce results differing by 5 kg or more for the same person. More importantly, none of these formulas were originally designed to tell you what you should weigh for health. They were designed for drug dosing.
This guide explains the four clinical IBW formulas — Hamwi, Devine, Robinson, and Miller — where each originated, what each calculates, worked examples for both a woman and a man, how they compare to a BMI-based healthy weight range, and what they genuinely cannot tell you.
Where Did "Ideal Body Weight" Come From?
The term entered clinical medicine in 1964 when G. J. Hamwi proposed a simple rule of thumb for estimating appropriate weight in diabetes management. In 1974, B. J. Devine adapted Hamwi's values — converting them to metric — for calculating gentamicin antibiotic doses in patients with renal impairment. Because drug clearance correlates with lean body mass rather than total weight, an IBW estimate was needed to avoid overdosing heavier patients.
Two refinements followed in the pharmacy literature: Robinson et al. (1983) and Miller et al. (1983) published adjusted coefficients. All four formulas have since spread far beyond their pharmaceutical origins and are now widely used as general health reference targets — a purpose for which they were never specifically validated (Pai & Paloucek, 2000).
The Four IBW Formulas at a Glance
All four formulas use only two inputs: sex and height in inches. To convert centimetres to inches, divide by 2.54. "Inches over 5 feet" means total height in inches minus 60.
| Formula | Year | Men (kg) | Women (kg) |
|---|---|---|---|
| Hamwi | 1964 | 48 + 2.7 × (Hin − 60) | 45.5 + 2.3 × (Hin − 60) |
| Devine | 1974 | 50 + 2.3 × (Hin − 60) | 45.5 + 2.3 × (Hin − 60) |
| Robinson | 1983 | 52 + 1.9 × (Hin − 60) | 49 + 1.7 × (Hin − 60) |
| Miller | 1983 | 56.2 + 1.41 × (Hin − 60) | 53.1 + 1.36 × (Hin − 60) |
Hin = height in inches. To convert cm → inches: divide by 2.54.
One historical detail worth noting: for women, Hamwi and Devine give identical results. Devine converted Hamwi's women's values (100 lbs base + 5 lbs/inch) directly into metric (45.5 kg + 2.3 kg/inch) without modification. The men's formulas diverge — Hamwi gives higher results at average heights because it uses a larger per-inch increment (2.7 vs 2.3 kg).
Each Formula Explained
Hamwi (1964)
Women: IBW = 45.5 + 2.3 × (height_inches − 60)
Original values in pounds: 106 lbs + 6 lbs/inch for men; 100 lbs + 5 lbs/inch for women. Proposed as a clinical reference for diabetes management — the earliest of the four formulas.
Devine (1974)
Women: IBW = 45.5 + 2.3 × (height_inches − 60)
The most widely used IBW formula in clinical settings today. Developed for gentamicin dosing in renal impairment. The women's formula is mathematically identical to Hamwi; the men's formula uses 50 kg base and 2.3 kg/inch rather than Hamwi's 48 kg and 2.7 kg/inch.
Robinson (1983)
Women: IBW = 49 + 1.7 × (height_inches − 60)
Published as a refined pharmacological alternative to Devine. Uses a higher base weight for both sexes but a smaller per-inch increment, producing moderately lower estimates than Hamwi at most heights.
Miller (1983)
Women: IBW = 53.1 + 1.36 × (height_inches − 60)
Uses the highest base weight and the smallest per-inch increment of all four formulas. Produces higher estimates at shorter heights but converges with — or falls below — the others as height increases.
BMI-Based Healthy Weight Range
An alternative to the single-number IBW approach is calculating your healthy weight range using BMI 18.5–24.9 kg/m², which provides an upper and lower bound supported by population-level evidence. For a practical midpoint, Peterson et al. (2016) proposed using BMI 22 as an anchor — a value that closely aligns with the traditional IBW formula outputs at average heights.
BMI healthy weight range formula: weight (kg) = BMI × height (m)²
Worked Example: Woman, 165 cm (5 ft 5 in)
165 ÷ 2.54 = 64.96 ≈ 65 inches. Inches over 5 ft: 65 − 60 = 5.
All four formulas cluster between 57.0 and 59.9 kg — a spread of only 2.9 kg. The BMI-22 midpoint of ~60 kg sits just above the cluster. All results fall comfortably within the healthy BMI range of 50.4–67.8 kg.
Worked Example: Man, 178 cm (5 ft 10 in)
178 ÷ 2.54 = 70.08 ≈ 70 inches. Inches over 5 ft: 70 − 60 = 10.
For men at 178 cm, the four formulas spread wider — a 4.7 kg range from 70.3 kg (Miller) to 75.0 kg (Hamwi). The larger per-inch increment in the Hamwi formula (2.7 kg vs 1.41 kg in Miller) drives this divergence over 10 inches. All results fall within the healthy BMI range of 58.6–78.9 kg.
Why the Formulas Disagree
Each formula was derived independently from different reference populations and methods, producing different base weights and per-inch increments:
- Base weight (IBW at exactly 5 ft / 60 inches): ranges from 45.5 kg (women, Devine/Hamwi) to 56.2 kg (men, Miller). Miller's high base produces higher estimates at shorter heights.
- Per-inch increment: Hamwi uses 2.7 kg/inch for men (highest), Miller uses 1.41 kg/inch (lowest). At 10 inches above baseline, this difference contributes: (2.7 − 1.41) × 10 = 12.9 kg, partially offset by Miller's higher base weight of 56.2 vs 48 kg (+8.2 kg), yielding a net spread of ~4.7 kg.
- No explicit BMI target: none of the formulas were anchored to a specific BMI. In practice they roughly correspond to BMI 20–22 for people of average height, but the correspondence weakens at extreme heights.
What These Formulas Cannot Tell You
All four IBW formulas use only sex and height. They do not account for:
Body composition — a muscular athlete and a sedentary person of the same height will receive identical IBW estimates, despite very different body fat percentages and health profiles.
Age — Flegal et al. (2013) in JAMA found that the BMI range associated with lowest all-cause mortality shifts slightly upward in older adults. Fixed IBW formulas make no age adjustment.
Ethnicity — Asian populations show increased cardiometabolic risk at lower weights than the thresholds implied by these formulas, consistent with revised BMI cut-offs from the WHO Expert Consultation (2004).
Frame size — older IBW tables sometimes adjusted for small, medium, or large frame, but this approach has largely been abandoned due to poor measurement reliability.
Research by Romero-Corral et al. (2010) in the European Heart Journal found that approximately 29.6% of US adults with a "normal" BMI (18.5–24.9) were classified as overfat by DEXA — illustrating the broader point that weight-based metrics, including IBW, can miss the variable that actually matters most: body fat percentage relative to lean mass.
What Matters More Than the Number
IBW and BMI are useful quick reference tools but neither provides a complete health picture. For most people, more meaningful indicators include:
- Body fat percentage — directly measures the fat-to-lean ratio. The US Navy circumference method provides a reasonable estimate without equipment (±3–5% accuracy). See How to Calculate Body Fat Percentage.
- Waist circumference — visceral (abdominal) fat is more strongly associated with cardiometabolic risk than total body weight. Thresholds associated with increased risk: >88 cm for women, >102 cm for men (NIH/NHLBI, 1998).
- Direction of trend — whether weight, body fat %, and waist circumference are moving in a healthier direction over time is often more informative than any absolute value at a single point.
Key Takeaways
- The four IBW formulas (Hamwi, Devine, Robinson, Miller) were developed for drug dosing and clinical reference — not as personal health weight targets.
- For women, Hamwi and Devine give identical results; for men they diverge by up to ~5 kg at average heights.
- All four formulas roughly correspond to BMI 20–22, placing them in the lower half of the healthy BMI range (18.5–24.9).
- Taking the average of all four formulas provides a more robust midpoint estimate than any single formula.
- IBW does not account for body composition, age, or ethnicity — body fat percentage is a more complete measure for individuals.
- A BMI healthy weight range (18.5–24.9) provides flexibility and aligns with population-level evidence; IBW provides a single number that should be treated as a reference, not a target.
Frequently Asked Questions
In clinical practice, IBW is primarily used for weight-based drug dosing (particularly renally-cleared medications), ventilator tidal volume settings, and nutritional assessment reference. For these applications, any of the four formulas is generally acceptable. For personal weight management, IBW should be treated as one data point among several — not a prescriptive target. If your weight falls within the healthy BMI range (18.5–24.9) and your body fat percentage is within healthy limits, targeting a specific IBW number is unlikely to provide additional clinical benefit.
This information is for general educational purposes. Consult a qualified healthcare professional for personalised guidance on weight and body composition goals.
This article is provided for general educational purposes only. Individual body weight, composition, and health needs vary considerably. Ideal weight formulas are clinical reference tools, not personal weight targets. The information presented does not constitute medical or dietary advice. Please consult a qualified healthcare professional before making significant dietary or lifestyle changes, especially if you have a medical condition, are pregnant, or take medications.
References
- Hamwi, G. J. (1964). Therapy: Changing dietary concepts. In T. S. Danowski (Ed.), Diabetes mellitus: Diagnosis and treatment (pp. 73–78). American Diabetes Association.
- Devine, B. J. (1974). Gentamicin therapy. Drug Intelligence and Clinical Pharmacy, 8(11), 650–655.
- Robinson, J. D., Lupkiewicz, S. M., Palenik, L., Lopez, L. M., & Ariet, M. (1983). Determination of ideal body weight for drug dosage calculations. American Journal of Hospital Pharmacy, 40(6), 1016–1019.
- Pai, M. P., & Paloucek, F. P. (2000). The origin of the "ideal" body weight equations. Annals of Pharmacotherapy, 34(9), 1066–1069.
- Peterson, C. M., Thomas, D. M., Blackburn, G. L., & Heymsfield, S. B. (2016). Universal equation for estimating ideal body weight and body weight at any BMI. American Journal of Clinical Nutrition, 103(5), 1197–1203.
- Flegal, K. M., Kit, B. K., Orpana, H., & Graubard, B. I. (2013). Association of all-cause mortality with overweight and obesity using standard body mass index categories. JAMA, 309(1), 71–82.
- Romero-Corral, A., Somers, V. K., Sierra-Johnson, J., Thomas, R. J., Collazo-Clavell, M. L., Korinek, J., Boix, R., Orban, M., Sirven, J. I., & Lopez-Jimenez, F. (2010). Accuracy of body mass index in diagnosing obesity in the adult general population. European Heart Journal, 31(6), 737–743.
- World Health Organization. (2000). Obesity: Preventing and managing the global epidemic (WHO Technical Report Series No. 894). World Health Organization.