BMI Calculator
Body Mass Index — your weight relative to height
Your BMI
—kg/m²
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Frequently Asked Questions
What is BMI and how is it calculated?
BMI (Body Mass Index) = weight(kg) ÷ height(m)². For example, 70 kg at 1.75 m = 70 ÷ 3.0625 = 22.9. In imperial: BMI = (lbs × 703) ÷ inches². It's a quick screening tool used by WHO and CDC.
What is a healthy BMI for adults?
WHO defines healthy BMI as 18.5–24.9. Under 18.5 = underweight, 25–29.9 = overweight, 30+ = obese. Note: some Asian populations use lower thresholds (23 for overweight).
Why is my BMI high but I exercise a lot?
BMI doesn't distinguish between muscle and fat. Muscle is denser than fat, so athletes and bodybuilders often have "overweight" or "obese" BMIs despite very low body fat. Use body fat % or waist circumference for a more accurate picture.
What is BMI Prime?
BMI Prime = your BMI ÷ 25. A value of 1.0 means you're exactly at the upper edge of normal. Below 0.74 = underweight, 0.74–1.0 = normal, above 1.0 = overweight or obese. It shows proportional distance from the normal limit.
What is the Ponderal Index?
Ponderal Index = weight(kg) ÷ height(m)³. It's considered more accurate for very tall or very short individuals where BMI can be misleading. Healthy Ponderal Index: 11–15 kg/m³.
BMI Classification (WHO)
| Category | BMI |
|---|---|
| Severe Thinness | < 16 |
| Moderate Thinness | 16–17 |
| Mild Thinness | 17–18.5 |
| Normal Weight | 18.5–25 |
| Overweight | 25–30 |
| Obese Class I | 30–35 |
| Obese Class II | 35–40 |
| Obese Class III | > 40 |
⚠ BMI is a screening tool
BMI does not measure body fat directly. Athletes may have high BMI due to muscle mass. For a complete picture, combine BMI with waist circumference, body fat %, and a clinical assessment.
Healthy Weight by Height
| Height | Normal BMI range |
|---|---|
| 5'4" | 108–145 lbs |
| 5'6" | 115–154 lbs |
| 5'8" | 122–164 lbs |
| 5'10" | 129–174 lbs |
| 6'0" | 136–183 lbs |
| 6'2" | 144–194 lbs |
What is BMI?
Body Mass Index (BMI) is a value calculated from your height and weight that is used to categorize a person as underweight, normal weight, overweight, or obese. It was developed by Belgian mathematician Adolphe Quetelet in the 1830s and has since become the world\'s most widely used screening tool for weight status.
The World Health Organization (WHO), the CDC, and most national health agencies use BMI as a population-level metric. While not a perfect measure for individuals (especially athletes), it remains a fast, non-invasive, and cost-free first-line screening tool.
Health Risks of Overweight & Obesity
Carrying excess body weight — particularly around the abdomen — significantly increases the risk of many serious medical conditions. Studies consistently show that each 5-unit increase in BMI raises the risk of type 2 diabetes by 30% and cardiovascular disease by 25%.
Health Risks of Being Underweight
A BMI below 18.5 is associated with malnutrition, immune deficiency, and organ stress. In some cases, being underweight carries similar mortality risks to being obese.
Limitations of BMI
Doesn't distinguish muscle from fat
A 200 lb athlete and a 200 lb sedentary person have the same BMI but very different health profiles. Muscular individuals often fall in the "overweight" category despite low body fat.
Ignores fat distribution
Visceral fat (around the organs) is far more dangerous than subcutaneous fat. Two people with the same BMI can have very different metabolic risk profiles depending on where they carry weight.
Age and sex variation
Women naturally carry more body fat than men at the same BMI. Older adults tend to lose muscle and gain fat, so their BMI may understate their true adiposity.
Ethnic differences
Asian populations tend to develop metabolic diseases at lower BMIs. Adjusted thresholds: overweight ≥23, obese ≥27.5 for Asian adults.