BMI Calculator
BMI Calculator
Calculate your Body Mass Index and health status
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BMI: What the Numbers Actually Mean
BMI = weight (kg) ÷ height (m)². Or in pounds: weight × 703 ÷ height² (inches). A 5'9" person at 170 lbs = BMI 25.1 (overweight). Same person at 169 lbs = 24.9 (normal). One pound difference changes your classification.
BMI was invented in 1832 for population statistics, not individual health. It can't distinguish muscle from fat—bodybuilders register as "obese," elderly with muscle loss as "healthy." Better indicators: waist circumference, body fat %, blood pressure, cholesterol. But BMI remains standard because it's simple and free.
BMI Categories
| BMI Range | Category | Health Risk |
|---|---|---|
| < 18.5 | Underweight | Malnutrition, weak immune system, osteoporosis |
| 18.5 - 24.9 | Normal | Lowest mortality risk |
| 25.0 - 29.9 | Overweight | Increased risk heart disease, diabetes |
| 30.0 - 34.9 | Obese Class I | High risk chronic disease |
| 35.0 - 39.9 | Obese Class II | Very high risk |
| ≥ 40.0 | Obese Class III | Extremely high risk, life-threatening |
BMI Limitations
Doesn't Account For
- Muscle mass: Athletes labeled "overweight"
- Age: Older adults lose muscle, appear healthier
- Sex: Women naturally have more body fat
- Ethnicity: Asians have higher risk at lower BMI
- Fat distribution: Belly fat worse than leg fat
Better Health Indicators
- Waist circumference: >40" men, >35" women = risk
- Waist-to-hip ratio: Central obesity marker
- Body fat %: 25%+ men, 32%+ women = high
- Blood tests: Glucose, cholesterol, inflammation
- Blood pressure: <120/80 optimal
Quick Weight Goals
5'4" (163 cm)
- Normal weight: 108-145 lbs
- Overweight starts: 146 lbs
- Obese starts: 175 lbs
5'9" (175 cm)
- Normal weight: 125-169 lbs
- Overweight starts: 170 lbs
- Obese starts: 203 lbs
6'0" (183 cm)
- Normal weight: 140-183 lbs
- Overweight starts: 184 lbs
- Obese starts: 221 lbs
6'2" (188 cm)
- Normal weight: 148-194 lbs
- Overweight starts: 195 lbs
- Obese starts: 234 lbs
Action Steps by Category
Underweight (BMI < 18.5)
See doctor to rule out medical causes. Increase calories with nutrient-dense foods. Strength training to build muscle.
Normal Weight (BMI 18.5-24.9)
Maintain with balanced diet and 150+ minutes weekly moderate exercise. Monitor waist size annually.
Overweight (BMI 25-29.9)
Lose 5-10% body weight to reduce health risks. Cut 500 calories/day = 1 lb/week loss. Check blood pressure and cholesterol.
Obese (BMI ≥ 30)
Consult doctor before starting diet. Screen for diabetes, sleep apnea. Consider medical weight loss programs. Even 5% weight loss improves health markers significantly.
Frequently Asked Questions
For populations: Yes. Good screening tool
For individuals: Sometimes wrong. Doesn't measure body fat directly
18.5-24.9 is considered normal weight
Lowest mortality risk typically at BMI 22-23
BMI only measures weight vs height, not muscle vs fat
Athletes with low body fat can be classified "overweight" or "obese"
Standard BMI: Adults 20-65 use same ranges
Children: Use age/sex-specific percentile charts
Waist circumference: Best predictor of health risk
Body fat %: More accurate than BMI for fitness
Yes. BMI under 18.5 = underweight
Risks: weak immune system, osteoporosis, fertility issues
Safe rate: 1-2 lbs per week
Even 5-10% weight loss significantly improves health
Yes. Asian populations have health risks at lower BMI
WHO recommends 23-27.5 range for Asian adults vs 25-30 for others
Better: Track waist circumference + how clothes fit
Weight/BMI fluctuates daily. Measure weekly at same time
- BMI over 30 (screen for diabetes, sleep apnea)
- BMI under 18.5 (rule out medical causes)
- Rapid weight change (10+ lbs in month)