BMI Calculator for Adults — Body Mass Index
Last reviewed: April 2026
The Body Mass Index (BMI) calculator estimates a screening number derived from your height and weight. Developed in the 1830s by mathematician Adolphe Quetelet, BMI uses the formula weight (kg) ÷ height (m)² to place adults into one of four categories: underweight, normal weight, overweight, or obese. It is widely used by healthcare providers as an initial screening tool because it's quick and requires no equipment. However, BMI has well-documented limitations — it does not distinguish between muscle mass and fat, it does not account for age, ethnicity, or bone density, and a person with high muscle mass may be classified as "overweight" despite being very fit. Use this calculator for general reference only, and discuss your results with a healthcare provider for context.
Calculate Your BMI
What this means
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| Category | BMI Range | Description |
|---|---|---|
| Underweight | Below 18.5 | May indicate nutritional deficiency or other health issues |
| Normal Weight | 18.5 – 24.9 | Associated with lowest risk for weight-related conditions |
| Overweight | 25.0 – 29.9 | Elevated risk for cardiovascular disease and diabetes |
| Obese | 30.0 and above | Higher risk for serious health conditions; consult your doctor |
Your BMI on the Full Spectrum
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Imperial equivalent: BMI = (weight in lbs × 703) ÷ height in inches²
Source: World Health Organization, National Institutes of Health
Known Limitations of BMI
BMI is a population-level screening tool, not a direct measure of body fat or health. It does not account for:
Muscle mass: Athletes with high muscle mass often register as "overweight" or even "obese" by BMI despite having very low body fat. Age & sex: Older adults tend to carry more fat at the same BMI. Women generally have more fat than men at the same BMI. Ethnicity: Studies show that people of Asian descent face higher health risks at lower BMI thresholds. Fat distribution: Where fat is stored (abdomen vs. hips) matters significantly for health risk — BMI doesn't capture this. For a more complete picture, consider waist circumference, waist-to-hip ratio, or body fat percentage measurements.
Frequently Asked Questions
What is a healthy BMI for adults?
For most adults, a BMI between 18.5 and 24.9 is classified as the "normal weight" range by the World Health Organization. Below 18.5 is underweight, 25.0–29.9 is overweight, and 30.0 or above is obese. These cutoffs are population-level screening thresholds, not individual diagnoses — a person can be healthy outside the normal range and unhealthy within it. Waist circumference, blood pressure, blood sugar, and cholesterol give a fuller picture of metabolic health.
How do I calculate BMI manually?
Metric: divide your weight in kilograms by your height in meters squared (BMI = kg ÷ m²). Imperial: multiply your weight in pounds by 703, then divide by your height in inches squared. For example, someone who is 5'10" (70 inches) and 180 lbs: (180 × 703) ÷ (70 × 70) = 25.8.
Is BMI accurate for athletes and muscular people?
No — BMI cannot distinguish muscle from fat, so muscular people often register as "overweight" or even "obese" despite low body fat. If you strength train regularly, a body fat percentage estimate (such as the US Navy tape-measure method) or waist-to-height ratio is a more meaningful measure than BMI.
Does this BMI calculator work for children and teens?
No. Adult BMI categories do not apply to anyone under 20. Children and teens are assessed using BMI-for-age percentiles, which compare a child's BMI to others of the same age and sex using CDC growth charts. Use our dedicated kids and teens BMI calculator for ages 2–19 instead.
Sources & Methodology
Formula: BMI = weight (kg) ÷ height (m)². Imperial: BMI = (weight in lbs × 703) ÷ height in inches².
Categories: Underweight <18.5 · Normal Weight 18.5–24.9 · Overweight 25.0–29.9 · Obese ≥30.0.
Sources: World Health Organization (WHO) BMI classification; National Institutes of Health (NIH) Clinical Guidelines on Obesity (1998). BMI is a population-level screening tool and does not directly measure body fat or health status.
Last reviewed: April 2026