Enter height to see range.
Calories/day at rest.
| Underweight | < 18.5 | |
| Normal Weight | 18.5 – 24.9 | |
| Overweight | 25.0 – 29.9 | |
| Obesity | ≥ 30.0 |
Body Mass Index (BMI) is a widely used screening tool that estimates body fat based on a person's weight relative to their height. Invented by Adolphe Quetelet in the 1830s, it remains the standard metric for health organizations like the WHO and CDC to categorize weight status.
While it doesn't measure body fat directly (like a caliper scan), it correlates strongly with direct measures. Health professionals use it to screen for weight categories that may lead to health problems.
For most adults (ages 20+), BMI falls into one of the following standard categories established by the World Health Organization (WHO):
| Category | BMI Range | Meaning |
|---|---|---|
| Underweight | < 18.5 | Possible malnutrition |
| Normal | 18.5 – 24.9 | Lowest health risk |
| Overweight | 25.0 – 29.9 | Increased cardiac load |
| Obesity (I, II, III) | ≥ 30.0 | High risk of disease |
The formula is the same for both. However, women naturally have more body fat than men at the same BMI. Men tend to have more muscle mass, which can sometimes skew results (making them appear overweight when they are muscular).
Older adults often lose muscle mass. A slightly higher BMI (25-27) is sometimes considered protective against osteoporosis and frailty in this age group.
Do not use adult charts! Kids are growing, so their BMI is compared against percentiles for their specific age and gender (e.g., "95th percentile").
Excess weight puts strain on your organs and joints. Common associated conditions:
Being underweight indicates possible nutritional deficiencies. Risks include:
BMI is a simple tool, not a diagnostic one. It fails to distinguish between:
Pro Tip: Use BMI alongside other metrics like Waist-to-Hip Ratio and Body Fat Percentage for a complete picture.
For adults 20-65, the target is 18.5 - 24.9. After age 65, a slightly higher range (up to 27) may be acceptable to preserve muscle mass and bone density.
The calculation is identical. However, women naturally carry more essential body fat than men, so a woman and a man with the same BMI will likely have different body compositions.
Yes, if the weight comes from lean muscle rather than fat (e.g., athletes). However, for the general population, a high BMI is strongly linked to health risks.
No. BMI is a simple calculation based on height and weight. It correlates with body fat but doesn't measure it directly like skinfold calipers or DEXA scans do.
Health risks may vary by ethnicity. For example, some Asian populations may experience health risks at a lower BMI (often starting at 23 instead of 25).