Calculate your Body Mass Index using metric or imperial units
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Category
BMI Range
Underweight
Below 18.5
Normal weight
18.5 – 24.9
Overweight
25 – 29.9
Obese (Class I)
30 – 34.9
Obese (Class II+)
35 and above
Disclaimer: BMI is a screening tool, not a diagnostic measure. It does not account for muscle mass, bone density, age, sex, or ethnicity. Consult a healthcare professional for a proper health assessment.
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What is BMI?
Body Mass Index (BMI) is a numerical value derived from a person's weight and height. It was developed by Belgian statistician Adolphe Quetelet in the 19th century and is used by the World Health Organization (WHO) as a screening tool to identify whether a person is underweight, at a healthy weight, overweight, or obese.
The formula is straightforward: BMI = weight (kg) ÷ height² (m). In imperial units: BMI = 703 × weight (lb) ÷ height² (in). The result places a person into one of several WHO categories.
It's important to understand that BMI is a population-level tool, not an individual diagnostic. A person with high muscle mass (such as an athlete) can have a "high" BMI while being perfectly healthy, and BMI does not account for fat distribution, which also matters for health risk.
How to Calculate BMI
Select your preferred unit system: metric (kilograms and centimeters) or imperial (pounds and feet/inches).
Enter your height and weight in the fields above.
Your BMI appears instantly with your WHO category and a visual indicator on the scale.
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Frequently Asked Questions
According to the World Health Organization, a BMI between 18.5 and 24.9 is considered a healthy or "normal" weight for most adults. Below 18.5 is classified as underweight. 25–29.9 is overweight, and 30 or above is classified as obese (with further sub-categories at 35 and 40). These thresholds apply to most adults aged 18–65.
No — BMI is a known limitation for muscular individuals. Since BMI only uses weight and height, it cannot distinguish between fat mass and muscle mass. A professional athlete might have a BMI in the "overweight" range while having very low body fat and excellent health. Similarly, an older person could have a "normal" BMI while having high body fat (a condition called "skinny fat"). For athletes, body composition measurements are more accurate.
Standard adult BMI thresholds do not apply to children and teenagers. For people under 18, BMI must be interpreted using age- and sex-specific percentile charts (BMI-for-age). A child with the same BMI as an adult may fall into a completely different category. This calculator is designed for adults 18 and older.
Metric: BMI = weight (kg) ÷ [height (m)]². For example, a person who is 70 kg and 1.75 m tall: BMI = 70 ÷ (1.75)² = 70 ÷ 3.0625 ≈ 22.9. Imperial: BMI = 703 × weight (lb) ÷ [height (in)]². For example, 154 lb at 5 ft 9 in (69 inches): BMI = 703 × 154 ÷ (69)² ≈ 22.7. Both formulas yield the same result when units are consistent.
To reach a BMI of 18.5 (low end of healthy): target weight = 18.5 × height² (m). To reach a BMI of 24.9 (high end of healthy): target weight = 24.9 × height² (m). For example, at 1.75 m height, the healthy weight range is 18.5 × 3.06 = 56.6 kg to 24.9 × 3.06 = 76.2 kg. Any weight loss goal should be discussed with a healthcare professional.