BMI Calculator

What is BMI (Body Mass Index)?

Body Mass Index (BMI) is a widely used screening tool that estimates body fat based on your weight and height. Developed by Belgian mathematician Adolphe Quetelet in the 1830s, BMI provides a simple numeric measure that allows health professionals to discuss weight problems objectively.

While BMI doesn't directly measure body fat, it correlates with more direct measures of body fat such as underwater weighing and dual-energy X-ray absorptiometry (DEXA scans). It's used as an inexpensive and easy-to-perform screening method for weight categories that may lead to health problems.

BMI Categories (WHO Classification)

BMI Range	Category	Health Risk
Below 16.0	Severe Thinness	High
16.0 – 16.9	Moderate Thinness	Moderate
17.0 – 18.4	Mild Thinness	Low
18.5 – 24.9	Normal Weight	Low
25.0 – 29.9	Overweight	Increased
30.0 – 34.9	Obese Class I	High
35.0 – 39.9	Obese Class II	Very High
40.0 and above	Obese Class III	Extremely High

How BMI is Calculated

The formula for BMI is straightforward:

• Metric: BMI = weight (kg) ÷ height (m)²
• Imperial: BMI = (weight (lbs) × 703) ÷ height (inches)²

For example, a person who weighs 70 kg and is 1.75 m tall would have a BMI of 70 / (1.75 × 1.75) = 22.86, which falls in the "Normal Weight" category.

Limitations of BMI

BMI is a useful population-level measure but has important limitations for individuals:

• Muscle mass: Athletes and muscular individuals may have a high BMI without excess body fat
• Age: Older adults may have more body fat at the same BMI compared to younger adults
• Gender: Women typically have more body fat than men at an equivalent BMI
• Ethnicity: BMI cutoffs may differ across ethnic groups; Asian populations may have higher health risks at lower BMI values
• Body fat distribution: BMI doesn't account for where fat is stored (visceral fat around organs is more dangerous than subcutaneous fat)

BMI Prime

BMI Prime is the ratio of your BMI to the upper limit of the "normal" BMI range (25 kg/m²). A BMI Prime of 1.0 means your BMI is exactly at the upper boundary of normal. Values below 1.0 indicate normal weight, while values above 1.0 indicate overweight or obesity. This makes it easier to see how far above or below the healthy range you are.