BMI Calculator

Calculate your Body Mass Index in metric or imperial units.

How to use this tool

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Open BMI Calculator
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FAQ

Is BMI an accurate health measure?
BMI is a useful screening tool but does not account for muscle mass, bone density, or distribution of fat.
What are the BMI categories?
WHO classifications: 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 and above).
Why does BMI differ between adults and children?
For children and teens (ages 2–19), BMI is interpreted using age- and sex-specific percentile charts, not fixed thresholds. The same BMI value means different things at different ages during development.
Can a fit person have a high BMI?
Yes. Athletes with high muscle mass often have a "overweight" BMI despite low body fat. This is a known limitation of BMI, which measures weight relative to height but cannot distinguish muscle from fat.
What is a better measurement than BMI?
Waist-to-height ratio and waist circumference are better predictors of metabolic risk. Body fat percentage measured by DEXA scan is the most accurate, but also the most expensive.

About BMI Calculator

BMI (Body Mass Index) is a screening tool that estimates body fatness based on weight and height. It was developed by Belgian mathematician Adolphe Quetelet in the 1830s and adopted by the World Health Organization as a population-level health screening metric. While BMI does not directly measure body fat, it correlates well with body fat at the population level and is used globally as a quick, cost-free health screen.

The BMI Formula

BMI is calculated as weight (kg) ÷ height (m)2. In imperial units: (weight in pounds × 703) ÷ height in inches2. A person who is 70 kg and 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9, which falls in the "Normal weight" range (18.5–24.9).

BMI Categories (WHO)

The World Health Organization defines BMI ranges as: Underweight (below 18.5), Normal weight (18.5–24.9), Overweight (25.0–29.9), and Obese (30.0 and above, subdivided into three classes). Some Asian populations have higher metabolic risk at lower BMI values, leading health authorities in several countries to use lower cutoff points (e.g., overweight starting at 23).

The Limitations of BMI

BMI is a proxy, not a diagnosis. It cannot distinguish muscle from fat, so a heavily muscled athlete may register as "overweight" despite having very low body fat. It also does not account for fat distribution — visceral fat (around the organs) carries far more metabolic risk than subcutaneous fat (under the skin). For a more complete picture, pair your BMI with waist circumference: a waist above 94 cm for men or 80 cm for women signals elevated cardiovascular risk regardless of BMI. Always discuss your results with a healthcare provider before drawing clinical conclusions.

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