📋 Table of Contents
BMI: The Most Common Method
Body Mass Index (BMI) is a ratio of weight to height squared. It was developed by Belgian mathematician Adolphe Quetelet in the 1800s and adopted by health organizations as a population-level screening tool.
Formula: BMI = weight (kg) ÷ height² (m²)
For a healthy BMI of 18.5–24.9, you can calculate the corresponding ideal weight range:
- Minimum healthy weight = 18.5 × height² (m²)
- Maximum healthy weight = 24.9 × height² (m²)
BMI Categories
| BMI | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Increased risk of malnutrition, osteoporosis |
| 18.5 – 24.9 | Normal weight | Lowest risk range |
| 25.0 – 29.9 | Overweight | Moderately increased risk |
| 30.0 – 34.9 | Obese (Class I) | High risk |
| 35.0 – 39.9 | Obese (Class II) | Very high risk |
| 40+ | Obese (Class III) | Extremely high risk |
BMI Limitations
- Ignores muscle mass — a muscular athlete may have "obese" BMI despite low body fat
- Ignores fat distribution — waist-to-hip ratio predicts cardiovascular risk better
- Not sex-adjusted — women naturally carry more fat than men at the same BMI
- Not age-adjusted — older adults lose muscle and gain fat without BMI changing
- Ethnicity differences — Asian populations have higher metabolic risk at lower BMI levels
Hamwi Formula
Developed by Dr. G.J. Hamwi in 1964, this formula was designed for clinical use in calculating drug dosages and caloric needs:
- Men: 106 lb for first 5 ft, then +6 lb per inch above 5 ft
- Women: 100 lb for first 5 ft, then +5 lb per inch above 5 ft
Example (5'10" male): 106 + (10 × 6) = 106 + 60 = 166 lb
The Hamwi formula gives a single target number rather than a range — useful as a quick clinical reference, but not representative of individual variation in body composition.
Devine Formula
Published by Dr. B.J. Devine in 1974, also originally developed for pharmacological dosing:
- Men: 50 kg + 2.3 kg per inch above 5 ft
- Women: 45.5 kg + 2.3 kg per inch above 5 ft
Example (5'10" male): 50 + (10 × 2.3) = 50 + 23 = 73 kg (161 lb)
The Devine formula is widely used in medical settings for calculating ideal body weight for ventilator settings and drug dosing.
Robinson Formula
Published by J.D. Robinson in 1983 as an alternative to Devine:
- Men: 52 kg + 1.9 kg per inch above 5 ft
- Women: 49 kg + 1.7 kg per inch above 5 ft
Example (5'10" male): 52 + (10 × 1.9) = 52 + 19 = 71 kg (157 lb)
Body Composition Approach
Rather than calculating a target weight, the body composition approach defines "ideal" based on a healthy body fat percentage — making it the most individualized method.
Healthy Body Fat Ranges
| Category | Women | Men |
|---|---|---|
| Essential fat | 10–13% | 2–5% |
| Athletes | 14–20% | 6–13% |
| Fitness | 21–24% | 14–17% |
| Acceptable | 25–31% | 18–24% |
| Obese | 32%+ | 25%+ |
Ideal Weight Formula (body comp approach):
Lean Body Mass ÷ (1 − target body fat %)
For example: If you have 130 lb of lean mass and want 20% body fat:
Ideal weight = 130 ÷ (1 − 0.20) = 130 ÷ 0.80 = 162.5 lb
Method Comparison — 5'10" (178 cm) Male
| Method | Ideal Weight | Best Use |
|---|---|---|
| BMI (18.5–24.9) | 129–173 lb (range) | Population-level screening |
| Hamwi | 166 lb | Clinical drug dosing |
| Devine | 161 lb | Medical/ventilator reference |
| Robinson | 157 lb | Alternative clinical estimate |
| Body composition (18% BF target) | ~165 lb | Fitness & performance goals |
Which Method Should You Use?
- For general health screening: BMI is fine as a quick check, but interpret with context
- For fitness goals: Body composition is superior — focus on fat loss, not just weight loss
- For medical dosing: Your doctor will use Devine or Hamwi — don't worry about these
- For tracking progress: Combine weight + waist circumference + body fat % for the best picture