Ideal Weight Calculator — Compare Hamwi, Devine, Robinson, and Miller Formulas
Ideal body weight (IBW) is a clinical concept, not a beauty standard. These formulas were developed by medical researchers to give clinicians a quick, height-based weight estimate for drug dosing, ventilator settings, and nutritional calculations. This calculator computes IBW using all four major formulas — Hamwi, Devine, Robinson, and Miller — so you can see how they compare and understand which context each was designed for.
Where height_in is total height in inches. All formulas use 60 inches (5 feet) as the baseline and add a fixed increment per inch above. BMI-based IBW: 22 × height_m².
Why Different Formulas Exist
The four IBW formulas were not developed to answer the same question. Hamwi (1964) was created to estimate ideal weight for diabetic patients managing diet — it is the most conservative formula and produces the lowest IBW for shorter individuals. Devine (1974) was created specifically to dose the antibiotic gentamicin, which distributes poorly into fat tissue — it remains the dominant formula in pharmacology and critical care. Robinson (1983) and Miller (1983) used larger population datasets and statistical regression to better fit observed healthy weights, producing slightly different coefficients. Understanding origin matters: using Hamwi for drug dosing or Devine for dietary counseling may produce suboptimal results.
IBW vs Healthy Weight Range
IBW formulas produce a single point estimate — useful for clinical calculations where one number is needed. But a single number is not the full picture. The healthy weight range corresponding to BMI 18.5–24.9 is a span of roughly 40–50 lb for most adults. For a 5'10" male, the healthy range is 129–174 lb; Devine IBW is 166 lb. IBW falls at the upper end of the healthy range because it was designed for average-framed adults, not the full population distribution. A person at 150 lb is equally healthy by BMI, even though they are 16 lb below IBW.
Limitations of IBW Formulas
All four IBW formulas share critical limitations. They use only height and sex — ignoring age, body composition, muscle mass, bone density, and ethnicity. For heavily muscled individuals (athletes, bodybuilders), IBW will underestimate a 'healthy' weight significantly. For very tall or very short individuals, the linear extrapolation breaks down. IBW is not a personal health target; it is a calculation shortcut for clinical settings where speed matters more than precision. Using IBW as a fitness goal can be misleading, particularly for people with above-average muscle mass.
How Doctors Use IBW
In hospitals, IBW is used in several critical calculations. Mechanical ventilation: tidal volume is set at 6 mL/kg IBW for lung-protective ventilation in ARDS patients — using actual body weight would over-inflate lungs in obese patients. Drug dosing: renally-cleared drugs (vancomycin, gentamicin, digoxin) and hydrophilic drugs that do not distribute into fat use IBW rather than actual weight to avoid overdosing. Nutritional support: ICU nutrition teams set protein targets (typically 1.2–2.0 g/kg IBW/day) using IBW rather than actual weight for obese patients to avoid overfeeding.
Formula Comparison for a 5'10" (70 in) Male
- Hamwi: 48 + 2.7 × (70−60) = 48 + 27 = 75 kg (165 lb)
- Devine: 50 + 2.3 × (70−60) = 50 + 23 = 73 kg (161 lb)
- Robinson: 52 + 1.9 × (70−60) = 52 + 19 = 71 kg (157 lb)
- Miller: 56.2 + 1.41 × (70−60) = 56.2 + 14.1 = 70.3 kg (155 lb)
- BMI-based (22 × 1.778²): 22 × 3.16 = 69.5 kg (153 lb)
When IBW Is Used Clinically
- Mechanical ventilation (ARDS): Tidal volume = 6 mL × IBW (kg) — prevents ventilator-induced lung injury.
- Antibiotic dosing: Gentamicin, vancomycin, and other hydrophilic antibiotics are dosed on IBW or adjusted body weight.
- ICU nutrition: Protein and caloric targets for obese patients are based on IBW to avoid overfeeding.
- Chemotherapy: Some agents use body surface area calculated from IBW for obese patients.
- Renal dosing: Creatinine clearance calculations for drug dosing in obese patients use IBW-adjusted formulas.
Frequently Asked Questions
What is ideal body weight?
Ideal body weight (IBW) is a target weight calculated from height and sex, representing a statistically 'optimal' weight for skeletal frame. It is widely used in clinical medicine for drug dosing, ventilator settings, and nutritional support — not as a personal fitness goal or beauty standard.
How is ideal weight different from a healthy weight range?
IBW formulas produce a single number. A healthy weight range corresponds to a BMI of 18.5–24.9 — for a 5'10" male, that is roughly 129–174 lb. The Devine IBW for a 5'10" male is 166 lb, which falls within that range but is far more specific than the range itself.
Why are there different formulas for ideal weight?
Each formula was designed for a specific clinical purpose. Devine (1974) was created for gentamicin antibiotic dosing. Hamwi (1964) was developed for diabetes dietary management. Robinson (1983) and Miller (1983) refined these using updated population data. None was designed as a universal fitness target.
Is ideal body weight used in medicine?
Yes, daily. ICU ventilators use IBW to calculate tidal volume in lung-protective ventilation protocols (6 mL/kg IBW). Pharmacists use IBW to dose renally-cleared drugs like vancomycin and gentamicin. Nutrition support teams use it to set caloric and protein targets for tube-fed patients.
Which IBW formula is most accurate?
No single formula is universally superior. Devine is the most cited in pharmacology and critical care. Hamwi remains common in dietetics. All four formulas agree within 5 kg for average-height individuals — divergence increases for people under 5 ft or over 6'4".
Is the ideal weight formula accurate for athletes or very tall/short people?
No. IBW formulas were derived from average-height populations and do not account for muscle mass, body composition, or ethnicity. A heavily muscled athlete may appear 'overweight' by IBW despite very low body fat. People outside the 5–6'2" height range fall outside the formulas' intended population.
What is a healthy BMI range?
The WHO defines healthy BMI as 18.5–24.9. Below 18.5 is underweight; 25–29.9 is overweight; 30+ is obese. BMI = weight (kg) ÷ height (m)². Like IBW, BMI does not distinguish between muscle and fat mass, making it an imperfect metric for athletic individuals.