Last updated: May 2026
Calculate your Body Mass Index using WHO and CDC standards.
Your Measurements
Your BMI
BMI Categories (WHO / CDC)
| Underweight | Below 18.5 | |
| Normal weight | 18.5 – 24.9 | |
| Overweight | 25.0 – 29.9 | |
| Obese class I | 30.0 – 34.9 | |
| Obese class II | 35.0 – 39.9 | |
| Obese class III | 40.0 and above |
BMI formula (metric): BMI = weight(kg) ÷ height(m)². For imperial: BMI = 703 × weight(lbs) ÷ height(inches)².
Healthy weight range is calculated by finding the weight that gives a BMI of 18.5 (lower bound) and 24.9 (upper bound) for your height.
BMI classifications are the same for adult males and females per WHO/CDC guidelines. Children use age- and sex-specific percentile charts instead.
⚠️ BMI is a screening tool, not a diagnostic measure. It does not account for muscle mass, bone density, age-related changes, or distribution of fat. People with high muscle mass may have a high BMI without excess body fat. Consult a healthcare provider for a complete health assessment.
Body Mass Index (BMI) is a screening measure that estimates body fat based on height and weight. It uses one of two formulas depending on your unit system:
Worked example: A person who is 5 feet 10 inches (70 inches) and weighs 175 lbs: BMI = (175 x 703) / (70 squared) = 123,025 / 4,900 = 25.1 - placing them just into the Overweight category per CDC and WHO standards.
This calculator uses WHO and CDC classification thresholds: Underweight (below 18.5), Normal weight (18.5-24.9), Overweight (25-29.9), and Obese (30 and above). It also shows your healthy weight range - the span of weights that would keep you in the 18.5-24.9 BMI range for your height.
BMI is a population-level screening tool. It does not measure body fat directly and has known limitations for athletes, older adults, and certain ethnic groups.
For adults 20 and older, the CDC and WHO define a healthy BMI as 18.5 to 24.9. Below 18.5 is underweight; 25 to 29.9 is overweight; 30 and above is obese. These thresholds apply to both men and women, though some research suggests the optimal range may shift slightly with age and ethnicity.
BMI does not distinguish between fat mass and lean mass. A muscular athlete may have a BMI of 27 (technically overweight) with very low body fat, while someone with a normal BMI can carry excess abdominal fat. For a more complete picture, consider waist circumference, body fat percentage testing, or a DEXA scan.
Yes. For children and teens ages 2 to 19, BMI is plotted on age- and sex-specific growth charts and expressed as a percentile rather than a fixed category. A BMI at the 85th to 95th percentile is considered overweight for children; at the 95th percentile and above it is considered obese. This calculator is designed for adults only.
In metric units: BMI = weight in kilograms divided by (height in meters squared). For example, a 75 kg person who is 1.75 m tall has a BMI of 75 divided by 3.0625, which equals 24.5 - falling in the Normal weight range.
Body Mass Index is a screening tool developed in the 1830s by Belgian statistician Adolphe Quetelet. It divides weight in kilograms by height in meters squared to produce a single number that roughly correlates with body fatness at the population level. Public health agencies including the WHO and the CDC use these thresholds to track obesity trends and flag individuals who may benefit from further clinical evaluation.
BMI has significant limitations. It cannot distinguish fat mass from lean mass, which is why a heavyweight powerlifter can register as "obese" while carrying less than 15% body fat. It also does not indicate where fat is stored—visceral fat around the organs carries far more cardiovascular risk than subcutaneous fat under the skin. Despite these caveats, BMI remains a fast, free, and reasonably predictive first screen for most sedentary adults.
| BMI Range | Category | Health Risk | Notes |
|---|---|---|---|
| Under 18.5 | Underweight | Increased | Malnutrition, bone density, and immune function concerns |
| 18.5–24.9 | Normal Weight | Low | Associated with lowest all-cause mortality in large studies |
| 25.0–29.9 | Overweight | Moderate | Lifestyle changes recommended; consider waist circumference |
| 30.0–34.9 | Obese Class I | High | Medical evaluation advised; risk of metabolic syndrome rises |
| 35.0–39.9 | Obese Class II | Very High | Structured intervention recommended |
| 40.0+ | Obese Class III | Extremely High | Immediate medical attention; bariatric options often discussed |
What does BMI actually measure?
BMI measures the ratio of weight to height squared. It is a proxy for body fatness at the population level—not a direct measure of fat, muscle, or metabolic health. Two people with identical BMIs can have very different body compositions, fitness levels, and disease risks.
Why is BMI criticized by health experts?
Critics point out that BMI ignores fat distribution (visceral vs. subcutaneous), does not account for age-related muscle loss, and was derived from data on European men. Many researchers argue that waist-to-height ratio, waist circumference, or body fat percentage are more clinically useful for individual risk assessment.
Does BMI work for athletes?
Not reliably. Athletes with high muscle mass routinely score in the overweight or obese range despite having low body fat percentages. For anyone who trains seriously, a body composition test (DEXA scan, hydrostatic weighing, or skinfold calipers) gives a far more meaningful result than BMI alone.
Is there a different healthy BMI for women vs. men?
The standard WHO and CDC thresholds (18.5–24.9 for normal weight) apply to both sexes. However, women naturally carry more essential body fat than men, and some research suggests women may tolerate a slightly higher BMI without elevated cardiometabolic risk. Sex-specific BMI cutoffs are not yet in mainstream clinical guidelines.
What is BMI percentile and how is it used for children?
For children and teens ages 2–19, raw BMI values are converted to age- and sex-specific percentiles using CDC growth charts. A BMI at the 85th–94th percentile is classified as overweight; at or above the 95th percentile is obese. This percentile system accounts for the fact that healthy BMI changes substantially as children grow.