Hamwi vs Devine Ideal Weight Formula

The Hamwi formula: the first gender-specific IBW equation

Published by George J. Hamwi in 1964, this formula was the first to provide distinct ideal body weight calculations for men and women, which was significant for its time. For men: 48 kg (106 lb) for the first 5 feet + 2.7 kg (5 lb) for each additional inch. For women: 45.5 kg (100 lb) for the first 5 feet + 2.2 kg (4.5 lb) for each additional inch. Hamwi was designed primarily for clinical nutrition settings to assess whether a patient was underweight, at a healthy weight, or overweight. The formula uses smaller per-inch increments than Devine for women, producing a more conservative IBW estimate. For a 5'8" woman, Hamwi yields 54.6 kg (120.4 lb), while Devine yields 56.4 kg (124.4 lb).

The Devine formula: the clinical drug-dosing standard

Published by B.J. Devine in 1974, this formula quickly became the standard for estimating ideal body weight in pharmacology and clinical medicine. For men: 50 kg (106 lb) for the first 5 feet + 2.3 kg (6 lb) for each additional inch. For women: 45.5 kg (100 lb) for the first 5 feet + 2.3 kg (5 lb) for each additional inch. Devine uses larger per-inch increments for men (6 lb vs 5 lb) and equal per-inch increments for both genders (5 lb per inch for women, matching Hamwi's base). The formula is used extensively in calculating doses for drugs with narrow therapeutic windows, including aminoglycosides, theophylline, and various chemotherapy agents, where dosing based on actual body weight can lead to toxicity.

Why do Hamwi and Devine give different results?

The two formulas differ in three key parameters: (1) the base weight for men — Hamwi uses 48 kg while Devine uses 50 kg, a 2 kg (4.4 lb) difference; (2) the per-inch increment for men — Hamwi uses 2.7 kg (5 lb) while Devine uses 2.3 kg (6 lb), meaning Devine adds more weight per inch of height; (3) the per-inch increment for women — both use similar values but Devine rounds to 5 lb per inch while Hamwi uses 4.5 lb per inch. For a 5'10" man: Hamwi = 71.6 kg vs Devine = 73.8 kg, a 2.2 kg (4.8 lb) difference. The higher Devine value reflects its pharmacological purpose: slightly higher IBW estimates are safer for drug dosing because underdosing is generally less dangerous than overdosing.

Clinical applications: when each formula is preferred

Use Devine when: calculating drug doses (especially aminoglycosides, vancomycin, theophylline); setting ventilator tidal volumes in critical care; estimating nutritional requirements in hospital settings. Devine is embedded in most clinical drug-dosing calculators and electronic health record systems. Use Hamwi when: assessing nutritional status in outpatient dietetics; setting caloric targets for weight management programs; providing a more conservative IBW estimate for general health assessments. Some dietitians prefer Hamwi for its lower weight targets, which may be more appropriate for weight management counseling in overweight populations.

Practical comparison examples

• 5'6" man: Hamwi = 63.4 kg (139.8 lb), Devine = 65.1 kg (143.4 lb) — Devine is 1.7 kg (3.6 lb) higher
• 5'10" man: Hamwi = 71.6 kg (157.8 lb), Devine = 73.8 kg (162.6 lb) — Devine is 2.2 kg (4.8 lb) higher
• 5'4" woman: Hamwi = 52.0 kg (114.7 lb), Devine = 52.0 kg (114.7 lb) — essentially identical at this height
• 5'8" woman: Hamwi = 54.6 kg (120.4 lb), Devine = 56.4 kg (124.4 lb) — Devine is 1.8 kg (4.0 lb) higher
• 6'0" man: Hamwi = 76.9 kg (169.5 lb), Devine = 78.6 kg (173.4 lb) — Devine is 1.7 kg (3.9 lb) higher