What is Ideal Body Weight?
Ideal body weight (IBW) is a calculated estimate of the weight that is associated with good health outcomes for a person of a given height and sex. Unlike BMI which assesses your current weight status, ideal weight gives you a target or reference point.
There are four major formulas used by healthcare providers, each developed independently with different methodologies. They tend to agree within a few kilograms for average heights but diverge at extreme heights.
The Four Formulas — How They Work
Devine Formula (1974):
Male: IBW = 50 kg + 2.3 kg × (height in inches − 60)
Female: IBW = 45.5 kg + 2.3 kg × (height in inches − 60)
Hamwi Formula (1964):
Male: IBW = 48 kg + 2.7 kg × (height in inches − 60)
Female: IBW = 45.5 kg + 2.2 kg × (height in inches − 60)
Robinson Formula (1983):
Male: IBW = 52 kg + 1.9 kg × (height in inches − 60)
Female: IBW = 49 kg + 1.7 kg × (height in inches − 60)
Miller Formula (1983):
Male: IBW = 56.2 kg + 1.41 kg × (height in inches − 60)
Female: IBW = 53.1 kg + 1.36 kg × (height in inches − 60)
Example for a 5'9" (175 cm) man (69 inches):
- Devine: 50 + 2.3 × (69 − 60) = 50 + 20.7 = 70.7 kg (156 lb)
- Hamwi: 48 + 2.7 × 9 = 48 + 24.3 = 72.3 kg (159 lb)
- Robinson: 52 + 1.9 × 9 = 52 + 17.1 = 69.1 kg (152 lb)
- Miller: 56.2 + 1.41 × 9 = 56.2 + 12.7 = 68.9 kg (152 lb)
Ideal Weight vs. BMI-Based Healthy Weight Range
The formula-based ideal weights above are single-point estimates. The BMI-based healthy weight range gives you a more practical window to aim for. A BMI of 18.5–24.9 is the range most associated with good health outcomes in large population studies.
For a 5'9" (175 cm) person, the BMI-healthy weight range is approximately 56.7–76.3 kg (125–168 lb). This gives you a 20 kg window — much more realistic to aim for than a single number, and more forgiving of natural variation in body composition.
Why These Formulas Were Originally Developed
It is important to understand the origin of these formulas. The Devine formula was created in 1974 specifically to estimate drug dosages in pharmacology — not as a weight loss target. Many medications are dosed based on lean body weight, and the Devine formula provided a quick way to estimate this.
The Hamwi formula (1964) was created by Dr. George Hamwi for insulin dosing in diabetic patients. The Robinson and Miller formulas are revisions of Devine, published in 1983 to refine the estimates.
None of these were designed as aesthetic weight targets. They describe approximate clinical reference points, not prescriptions for what any individual "should" weigh.
Limitations of Ideal Weight Calculators
They ignore body composition: Two people of the same height and weight can have very different percentages of muscle and fat. A muscular person may weigh more than their "ideal weight" while being metabolically healthy. A thin person may be at their "ideal weight" but have high visceral fat and poor metabolic markers.
They were developed on limited populations: Most formulas were derived from studies conducted in Western populations from decades ago. They may not accurately represent optimal weights for people of East Asian, South Asian, African, or other ancestries who have different body composition characteristics.
Frame size is not considered: Some people have genuinely larger or smaller bone frames. A large-framed person at their calculated "ideal weight" may actually be underweight in terms of lean mass.
Frequently Asked Questions
Which formula should I use as my weight goal?
Rather than picking one formula, look at the range across all four formulas — this gives you a reasonable target zone. Alternatively, use the BMI-based healthy range (18.5–24.9), which is broader and accounts for more individual variation. Consult your doctor for a personalized assessment that includes waist circumference and metabolic health markers.
What if my current weight is above all the ideal weight estimates?
These are estimates, not mandates. Even a 5–10% reduction from your current weight can significantly improve blood pressure, blood sugar, and cholesterol if you are overweight. Focus on gradual, sustainable changes rather than trying to reach an "ideal" number. Small, consistent improvements in lifestyle matter more than any target weight.
Why do the four formulas give different results?
Each formula was derived from different datasets, using different methodologies and patient populations. They weight height and sex differently. The divergence is greatest at heights well above or below the average (5'3"–5'9" range) where the formulas extrapolate beyond their original data.
Should height, age, and muscle mass affect ideal weight?
Age affects the formula indirectly through how body composition changes over time. These formulas only use height and sex, not age. Muscle mass is not captured — which is a significant limitation. More sophisticated assessment tools include measurements of lean body mass or waist circumference to account for body composition beyond just height and weight.