BMI Calculator

Calculate your Body Mass Index instantly — free, accurate, and easy to use.

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BMI Calculator

BMI Categories:

  • • Underweight: BMI less than 18.5
  • • Normal weight: BMI 18.5-24.9
  • • Overweight: BMI 25-29.9
  • • Obese: BMI 30 or greater

Note: BMI is a screening tool and does not diagnose body fatness or health. Consult with a healthcare provider for health assessments.

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What Is BMI?

Body Mass Index (BMI) is a numerical value derived from a person's weight and height. It is widely used as a simple screening tool to classify whether an individual falls into weight categories such as underweight, normal weight, overweight, or obese. Developed in the 19th century and adopted by the World Health Organization, BMI provides a quick, cost-free snapshot of weight status that is useful for population-level health assessments and initial clinical screening.

While BMI is convenient, it has well-known limitations. It does not directly measure body fat — a muscular athlete can have a high BMI yet carry very little fat, while an older adult with low muscle mass may fall in the "normal" range despite excess body fat. Ethnicity, age, and sex can also influence the health risks associated with a given BMI value. For these reasons, BMI should be considered a starting point for discussion with a healthcare provider, not a definitive health verdict.

How to Use This Calculator

  1. 1Enter your height — choose feet/inches for imperial or centimeters for metric.
  2. 2Enter your weight — choose pounds (lbs) for imperial or kilograms (kg) for metric.
  3. 3Click the Calculate button to get your result instantly.
  4. 4Review your BMI score and the corresponding weight category for context.

BMI Formula & Weight Categories

BMI (metric): BMI = weight(kg) / height(m)² BMI (imperial): BMI = 703 × weight(lb) / height(in)² Weight Categories (WHO): Under 18.5 → Underweight 18.5 – 24.9 → Normal weight 25.0 – 29.9 → Overweight 30.0 + → Obese

Classifications are based on WHO guidelines. BMI is a screening tool, not a diagnostic measure. A high or low BMI does not diagnose body fatness or overall health — consult a qualified healthcare provider for personalized medical advice.

Worked Examples

Example 1 — Normal Weight: 5′6″ / 140 lbs (168 cm / 63.5 kg)

Using the imperial formula: BMI = 703 × 140 ÷ 66² = 98,420 ÷ 4,356 ≈ 22.6. A BMI of 22.6 falls in the Normal weight range (18.5–24.9). This person's weight is proportionate to their height according to WHO standards.

Example 2 — Overweight: 5′10″ / 200 lbs (178 cm / 90.7 kg)

Using the imperial formula: BMI = 703 × 200 ÷ 70² = 140,600 ÷ 4,900 ≈ 28.7. A BMI of 28.7 falls in the Overweight range (25.0–29.9). While not in the obese category, this result suggests a conversation with a healthcare provider about weight management may be beneficial.

Example 3 — Obese (Class I): 6′0″ / 250 lbs (183 cm / 113.4 kg)

Using the imperial formula: BMI = 703 × 250 ÷ 72² = 175,750 ÷ 5,184 ≈ 33.9. A BMI of 33.9 falls in the Obese Class I range (30.0–34.9). This classification is associated with increased risk for conditions such as type 2 diabetes, hypertension, and cardiovascular disease.

Frequently Asked Questions

Is BMI accurate for athletes and muscular people?▾
Not always. BMI does not distinguish between fat mass and lean muscle mass. Highly trained athletes often have BMIs in the overweight or obese range despite having low body fat percentages. For athletes, body composition methods such as DEXA scans, skinfold calipers, or hydrostatic weighing give a much more accurate picture of health and fitness.
Is there a different healthy BMI range for women vs. men?▾
The standard WHO BMI categories (18.5–24.9 for normal weight) are the same for adult men and women. However, women typically carry a higher percentage of body fat than men at the same BMI, and health risks can differ by sex. Some researchers suggest sex-specific cutoffs, but they are not yet universally adopted in clinical practice.
How is BMI calculated differently for children?▾
For children and teenagers (ages 2–19), BMI is interpreted using age- and sex-specific percentile charts rather than fixed category cutoffs. A child's BMI is compared to peers of the same age and sex: below the 5th percentile is considered underweight, 5th–84th is healthy weight, 85th–94th is overweight, and 95th or above is obese. Adult BMI thresholds do not apply to children.
Can I have a normal BMI and still be unhealthy?▾
Yes. A person can have a BMI in the normal range while still carrying excess visceral (abdominal) fat, which is a strong predictor of metabolic disease. Conversely, waist circumference, blood pressure, blood glucose, cholesterol levels, and physical activity are all important health markers that BMI does not capture. BMI is a useful first screen, not a complete health assessment.
What is BMI Prime, and how is it different from regular BMI?▾
BMI Prime is a simple ratio of your actual BMI to the upper limit of the normal weight range (24.9). A BMI Prime of 1.0 means you are exactly at the upper boundary of normal weight; below 1.0 is normal or underweight, and above 1.0 indicates overweight or obese. It offers the same information as standard BMI but makes it immediately obvious how far a person is from the normal weight ceiling.