BMI Calculator

About BMI

The BMI Calculator facilitates the computation of Body Mass Index (BMI) and associated weight status, taking age into account. Utilize the "Metric Units" tab for International System of Units or the "Other Units" tab for converting units into either US or metric measures.

The calculator also determines the Ponderal Index, complementing BMI, and both are elaborated below.

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Introduction to BMI:

BMI gauges a person's leanness or corpulence based on height and weight, aiming to quantify tissue mass. It serves as a general indicator of healthy body weight for height. BMI categorizes individuals into underweight, normal weight, overweight, or obese, with varying ranges influenced by factors like region and age.

Although imperfect, BMI is valuable in prompting further testing or action to address health concerns.

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BMI Categories for Adults (World Health Organization):

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• Severe Thinness: < 16

• Moderate Thinness: 16 - 17

• Mild Thinness: 17 - 18.5

• Normal: 18.5 - 25

• Overweight: 25 - 30

• Obese Class I: 30 - 35

• Obese Class II: 35 - 40

• Obese Class III: > 40

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BMI Categories for Children and Teens (CDC):

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• Underweight: < 5%

• Healthy weight: 5% - 85%

• At risk of overweight: 85% - 95%

• Overweight: > 95%

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Risks Associated with Weight:

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• Risks of being overweight include high blood pressure, diabetes, heart disease, and mental health issues.

• Risks of being underweight encompass malnutrition, weakened immunity, and reproductive complications.

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Limitations of BMI:

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• BMI does not consider body composition, being an estimate of excess body weight.

• Factors like age, sex, and muscle mass affect BMI accuracy, especially in athletes.

• BMI for children is influenced by growth factors and fat-free mass.

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BMI Formula:

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• USC Units: BMI = 703 × (mass in lbs) / (height in inches)^2

• SI, Metric Units: BMI = (mass in kg) / (height in meters)^2

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BMI Prime: BMI prime assesses a person's BMI in relation to the upper limit of "normal" BMI (25 kg/m^2). The formula is BMI prime = BMI / 25. It yields a dimensionless value, with classifications such as underweight (< 0.74), normal (0.74 - 1), overweight (1 - 1.2), and obese (> 1.2). BMI prime offers a quick assessment of BMI deviation from the upper limit and allows comparisons between groups with different upper BMI limits.

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Ponderal Index (PI):

The Ponderal Index (PI) shares similarities with BMI as it assesses a person's leanness or corpulence based on height and weight. The primary distinction lies in the cubing rather than squaring of height in the formula (provided below).

While BMI is valuable for population-level assessments, it may lack precision when gauging leanness or corpulence on an individual basis. Despite similar limitations, the Ponderal Index proves more reliable for very tall or short individuals, offering more accurate results compared to BMI for individuals at the extremes of the height and weight spectrum.

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