Ideal Weight Calculator
Find your ideal body weight using four established formulas: Devine, Robinson, Miller, and Hamwi, with frame size adjustment.
Results
Visualization
How It Works
Ideal body weight formulas estimate a target weight from height and sex. The four formulas in this calculator come from different sources: Hamwi (1964) by George Hamwi for diabetic meal planning at Ohio State; Devine (1974) by B.J. Devine for aminoglycoside antibiotic dosing; Robinson (1983) by John Robinson refining Devine for non-pharmacologic use; and Miller (1983) by Donna Miller from a study of US Army personnel. None of these were validated against mortality or morbidity data; they're consensus estimates from clinical observation and pharmacokinetic needs. The four formulas typically span a 4-7 kg range for the same height, which is a useful reminder that ideal weight is a range, not a point. For non-pharmacologic purposes, BMI-based healthy weight ranges (BMI 18.5-24.9, with the lowest mortality at 22.5-25.0) are better grounded in epidemiologic evidence than these legacy formulas.
The Formula
Variables
- IBW — Ideal body weight in kilograms
- inches over 60 — Height in inches above 60 inches (152.4 cm)
- Frame factor — 0.9 small, 1.0 medium, 1.1 large skeletal frame
Worked Example
Sarah, 173 cm, female, medium frame. Inches over 60: (173 - 152.4) / 2.54 = 8.11 inches. Devine: 45.5 + (2.3 * 8.11) = 64.2 kg. Robinson: 49 + (1.7 * 8.11) = 62.8 kg. Miller: 53.1 + (1.36 * 8.11) = 64.1 kg. Hamwi: 45.5 + (2.2 * 8.11) = 63.3 kg. Frame adjustment is 1.0 (medium), no change. Average: (64.2 + 62.8 + 64.1 + 63.3) / 4 = 63.6 kg. The four formulas span a 1.4 kg range here, all clustering near 63 kg. For comparison, BMI 22.5 (mortality minimum) at 173 cm = 22.5 * 1.73^2 = 67.3 kg. The legacy formulas land 3-5 kg below the BMI mortality minimum, illustrating that they were derived from older, lower-weight reference populations and shouldn't be treated as health-optimized targets.
Methodology
The Hamwi formula (1964) was developed by George Hamwi for the American Diabetes Association as a quick mental-math tool for diabetic meal planning: men 106 lbs at 5 feet plus 6 lbs per inch; women 100 lbs at 5 feet plus 5 lbs per inch. The Devine formula (1974) by B.J. Devine generalized Hamwi's structure for aminoglycoside antibiotic pharmacokinetics, where dosing on actual body weight in obese patients risked nephrotoxicity and ototoxicity from drug accumulation in lean tissue. The Robinson formula (1983) and the Miller formula (1983) refined Devine using updated reference samples; Robinson drew from civilian outpatient data, Miller from US Army personnel. None of these formulas were validated against morbidity or mortality endpoints. Modern BMI-based healthy weight ranges (18.5-24.9 per WHO) are derived from large prospective cohort studies including the Prospective Studies Collaboration (2009, 894,576 subjects) which identified mortality nadirs at BMI 22.5-25.0. The frame size adjustment of plus or minus 10% comes from clinical convention dating to the 1959 Metropolitan Life Insurance height-weight tables and lacks rigorous validation, though correlations between elbow breadth, wrist circumference, and skeletal mass support its directional validity (Frisancho 1984).
When to Use This Calculator
Hospital pharmacists use Devine IBW to dose aminoglycosides (gentamicin, tobramycin, amikacin), which distribute predominantly in lean tissue and require IBW-based dosing in patients with BMI over 30 to avoid nephrotoxic peak concentrations. The 1991 NIH Consensus Conference on Bariatric Surgery established percent excess weight loss as the standard outcome metric, where excess weight equals current weight minus IBW. Insurance medical underwriters historically used IBW tables (Metropolitan Life 1959, 1983) for coverage decisions; this practice was largely replaced by BMI in the 1990s. Eating disorder treatment programs use IBW as one anchor for refeeding goal weights, typically targeting 90-95% of IBW as a minimum for medical stabilization in anorexia nervosa, with full weight restoration to historical pre-illness weight or BMI 20+.
Common Mistakes to Avoid
Treating Devine female IBW as a health target when it was designed for antibiotic dosing produces goals 2-4 kg below evidence-based BMI ranges. Picking the lowest of the four formulas as your target encourages underweight goals; pick the average. Ignoring the frame size adjustment for very small or very large skeletal builds can introduce 4-7 kg of error. Applying these formulas to people under 152 cm tall extrapolates outside the validation range; pediatric and short-stature reference data should be used instead. Setting goal weights based on what you weighed at age 20 doesn't account for normal age-related changes in bone density and muscle distribution; goals should be set on current physiology, not historical photos.
Practical Tips
- Estimate frame size from wrist circumference. For women under 165 cm: small under 14 cm, medium 14-15 cm, large over 15 cm. For women over 165 cm: small under 14.5, medium 14.5-15.5, large over 15.5. For men: small under 16.5, medium 16.5-19, large over 19 cm. (Frisancho method, Am J Clin Nutr 1984.)
- Pharmacists use Devine for aminoglycoside dosing in obese patients (gentamicin, tobramycin) because using actual body weight risks overdose; the drugs distribute primarily into lean tissue. The Devine value isn't a health target.
- BMI 22.5 lands above all four IBW formulas at heights over 160 cm. The 2009 Prospective Studies Collaboration meta-analysis (894,576 subjects) found mortality nadirs at BMI 22.5-25.0; aim there if you're under 65, not at the lower IBW values.
- Adults over 65 should aim higher. Multiple cohorts (Flicker et al., 2010 J Am Geriatr Soc) show lowest mortality at BMI 27-28 in older adults, possibly because mild excess weight protects against sarcopenia and offers reserves during illness.
- Bariatric programs use IBW to calculate percent excess weight loss (%EWL): %EWL = (preop weight - current weight) / (preop weight - IBW) * 100. A successful gastric bypass typically reaches 60-70% EWL by 18 months.
- Don't aim for the lowest of the four IBW values. Devine for women in particular, originally for drug dosing, sits 2-4 kg below modern BMI-based healthy weight ranges and isn't a health-optimized target.
Frequently Asked Questions
Which IBW formula should I use as my target?
None of them, alone. They were derived in the 1960s-1980s for specific clinical purposes (drug dosing, diabetic meal planning) and don't reflect modern epidemiologic mortality data. Use the average of all four as a rough orientation, then verify against BMI-based healthy weight ranges (BMI 18.5-24.9). The mortality minimum from the 2009 Lancet meta-analysis sits at BMI 22.5-25.0, often higher than these legacy IBW values.
Why do the formulas disagree by 4-7 kg?
Different reference populations and purposes. Hamwi (1964) was for quick diabetic meal planning. Devine (1974) was for antibiotic pharmacokinetics. Robinson and Miller (both 1983) were attempts to refine Devine using broader civilian and military samples. None used mortality endpoints. The 4-7 kg spread reflects how loose the historical consensus was, and is a good reminder that ideal weight is a range, not a point.
Does frame size matter?
Skeletal frame measured by elbow breadth or wrist circumference correlates with healthy weight (Frisancho, Am J Clin Nutr 1984), but the effect is smaller than the 10% common adjustment suggests. Large-framed adults can carry an extra 2-4 kg of bone and lean tissue versus small-framed adults of the same height. The wrist circumference method (small under 16.5 cm, large over 19 cm for men) is the most reproducible self-assessment.
Why are these formulas different for men and women?
Adult men have higher lean body mass (typically 80-85% of body weight versus 70-75% in women) and heavier average skeletal mass. The female base values (45.5 in Hamwi and Devine, 49 in Robinson, 53.1 in Miller) sit 4-6 kg below the male base values, reflecting these biological differences. The slope (kg per inch over 5 feet) is similar across sexes because incremental height adds similar lean tissue regardless of sex.
What about ideal weight for kids and teens?
Don't use these formulas. Pediatric weight assessment uses CDC growth charts that plot weight, height, and BMI against age- and sex-specific percentiles. Healthy weight is BMI between the 5th and 85th percentiles for age and sex. The American Academy of Pediatrics 2023 guidelines recommend evaluation at the 85th percentile and intervention at the 95th. WHO growth standards apply for children under 5.
How do bariatric programs use IBW?
To calculate percent excess weight loss (%EWL) after surgery. Excess weight = preoperative weight minus IBW. %EWL = (preop weight - current weight) / (preop weight - IBW) * 100. A 130 kg patient with IBW 70 kg who reaches 90 kg post-surgery has 40 kg of excess weight, lost 40 kg, and achieved 67% EWL. Successful gastric bypass typically delivers 60-70% EWL at 18 months; sleeve gastrectomy 50-60%; lap band 40-50% (with much higher revision rates).
What if my goal weight is below all four IBW values?
Investigate. A goal more than 5 kg below the average IBW for your height usually reflects body image concerns rather than health optimization. Mortality risk rises 30% per 5 BMI points below 22.5, mirroring the rise above 25. If you're targeting BMI under 18.5 for non-medical reasons, consult a clinician. Trained athletes legitimately compete at low weights for sport (jockeys, climbers, distance runners) under medical supervision; recreational dieting to those weights carries real risk.