About the Ideal Weight Calculator

Ideal Body Weight (IBW) is the weight historically associated with maximal life expectancy for a given height and sex. Four equations remain in clinical use, each derived from a different population and philosophical stance. This calculator reports all four side by side so you can compare and decide which fits your context.

The Devine formula (1974) was popularised for drug-dosing calculations (e.g., gentamicin, digoxin) and is the default IBW in many pharmacology references including the FDA, BNF, and the Sanford Guide. Robinson (1983), Hamwi (1964), and Miller were derived from insurance actuarial data linking body weight to longevity, with slightly different regression fits.

None of these formulas should be used in isolation. They are most useful as a starting point for clinical drug dosing (especially in obesity, where actual body weight may overdose hydrophilic drugs), as a comparison to BMI healthy-weight ranges, or as a sanity check before bariatric or nutritional consultations. For athletic populations, lean-body-mass estimation is more useful than IBW.

How It Works

All four formulas take the same general form: a base weight at 60 inches (5 feet), plus a per-inch increment above 60:

Devine:   Men 50   + 2.3  × (in - 60)    Women 45.5 + 2.3  × (in - 60)
Robinson: Men 52   + 1.9  × (in - 60)    Women 49   + 1.7  × (in - 60)
Hamwi:    Men 48   + 2.7  × (in - 60)    Women 45.5 + 2.2  × (in - 60)
Miller:   Men 56.2 + 1.41 × (in - 60)    Women 53.1 + 1.36 × (in - 60)

Devine and Hamwi give similar weights; Robinson and Miller trend lower. The Hamwi formula predates the others by 20 years and is the most generous (highest IBW), reflecting the larger average body habitus of mid-century actuarial populations.

The formulas are valid only for heights at or above 60 inches; for shorter adults, BMI-based healthy weight ranges are preferred. Outputs in kg are converted to lb using the factor 2.20462 lb/kg.

Worked Examples

A 5′10″ (70 in) male, over-60 increment = 10 in:

Devine: 50 + 23 = 73.0 kg (160.9 lb)
Robinson: 52 + 19 = 71.0 kg (156.5 lb)
Hamwi: 48 + 27 = 75.0 kg (165.3 lb)
Miller: 56.2 + 14.1 = 70.3 kg (155.0 lb)
Average: 72.3 kg (159.4 lb)

A 5′4″ (64 in) female, over-60 increment = 4 in:

Devine: 45.5 + 9.2 = 54.7 kg (120.6 lb)
Robinson: 49 + 6.8 = 55.8 kg (123.0 lb)
Hamwi: 45.5 + 8.8 = 54.3 kg (119.7 lb)
Miller: 53.1 + 5.44 = 58.5 kg (129.0 lb)

All four sit within the BMI 18.5-24.9 healthy range (47.4-63.9 kg at 1.60 m for the woman; 56.7-76.3 kg at 1.78 m for the man). The formulas are most useful for drug dosing, where Devine is the international default.

When to Use This Tool

Drug dosing for hydrophilic medications (gentamicin, vancomycin, digoxin) where actual body weight would overdose obese patients.
Nutritional assessment in eating-disorder recovery — IBW vs. actual weight informs treatment intensity.
Pre-bariatric surgery evaluation — IBW used in excess-weight-loss calculations.
ICU tidal-volume settings (6 mL/kg predicted body weight, ARDSNet protocol).
Clinical reference for adult growth-hormone deficiency work-up.
Cross-check against BMI healthy-weight range for sanity.
Insurance actuarial review (historical context only).

Limitations & Disclaimer

IBW formulas are derived from population averages and do not account for body composition, frame size, ethnicity, or athletic muscle mass. They are valid only for adults ≥5 ft tall. Drug-dosing decisions should follow current FDA, BNF, or institutional protocols. This tool is not medical advice; consult a licensed physician or pharmacist for individual dosing. See our disclaimer for full terms.

Frequently Asked Questions

Which IBW formula should I use?

Devine (1974) is the international default for drug dosing (FDA, BNF, Sanford Guide). Robinson (1983) and Miller are alternatives for nutrition assessment. Hamwi (1964) is older and more generous; some bariatric centres still use it. None is uniformly superior — report all four and pick the one suited to your clinical question.

What is ‘predicted body weight’ (PBW)?

PBW is a variation of IBW used for ICU ventilator settings (ARDSNet 2000). The formula is <code>PBW (male) = 50 + 0.91 × (cm - 152.4)</code> and <code>PBW (female) = 45.5 + 0.91 × (cm - 152.4)</code>. Tidal volume is set at 6 mL/kg PBW, not actual body weight, to prevent ventilator-induced lung injury.

Why does Devine give different weights for men and women?

Because at any given height, men have greater lean mass and bone density on average. The +5 (men) and -161 (women) intercepts mirror the gender dimorphism in the underlying data, similar to Mifflin-St Jeor’s intercepts for BMR.

Are IBW formulas accurate for muscular athletes?

No. A 1.85 m male bodybuilder at 100 kg is 27 kg above Devine IBW (73 kg) but may carry only 10% body fat. IBW formulas assume population-average body composition and underestimate the “healthy” weight of muscular individuals. Use lean-body-mass or body-fat % instead.

Why are the formulas valid only above 60 inches?

The base weight (50, 45.5, 52, 49, 48 kg) was derived from actuarial data on adults ≥5 ft. Extrapolating below 60 in gives nonsensical results (e.g., negative weights for very short adults). For shorter individuals, BMI-based healthy weight ranges are preferred.

How does IBW compare with BMI healthy range?

For most heights 60-78 in, IBW formulas produce weights that sit within the BMI 18.5-24.9 healthy range. The two metrics agree closely for average-build adults but diverge for very muscular or very lean individuals. BMI is the screening metric; IBW is the dosing reference.

Last updated: September 9, 2026 · Author: HT99 Tools Editorial Team