What Is Body Mass Index (BMI)? How Can We Calculate It?

Body mass index or BMI is a value derived from the mass and height of a person. BMI gives us an idea about the amount of fat a person have, by determining the ideal weight for a person’s height (based on a cutoff) and assuming that the excess weight is attributable to fat. To measure a person’s BMI, we have to divide a person’s weight in kilograms by his/her height in squared meters.

Calculation of BMI

Body Mass Index (BMI) Calculator

Body Mass Index (BMI) is a value derived from a person’s weight and height. It gives an indication about the amount of body fat and associated health risks. BMI is calculated by dividing weight in kilograms by height in meters squared (kg/m²).

Unit System: Metric (kg, cm) Imperial (lb, in)

Weight:

Height:

Calculate BMI

Your BMI: kg/m²

Category:

How your BMI was calculated:

BMI Category	BMI Range (kg/m²)
Underweight	Less than 18.5
Normal weight	18.5 to 24.9
Overweight	25.0 to 29.9
Obese	30.0 to 34.9
Morbidly Obese	35.0 or higher

Limitations of BMI:

• BMI is a proxy indicator that does not actually measure body fat directly
• Cannot differentiate between visceral or subcutaneous fat
• May overestimate body fat in athletes or those with muscular builds
• May underestimate body fat in older persons or those with muscle wasting
• Not suitable for pregnant women or growing children

Range of BMI

Limitations of BMI

• PROXY indicator (does not actually measure the fat mass, but makes an idea about it).
• Cannot differentiate between visceral or subcutaneous fat.
• BMI may overestimate (in athletes) or underestimate (in old age or muscle wasting) fat.
• Should not be used for pregnant women or growing children.

Alternatives to BMI Measurement

Skinfold Thickness

This method uses calipers to measure the thickness of subcutaneous fat at specific body sites (such as triceps, subscapular, and suprailiac areas). The measurements are then used in predictive equations to estimate total body fat percentage. This method is more direct than BMI as it actually measures fat, rather than using weight as a proxy.

Waist Circumference

A simple measurement of the circumference around the waist (usually at the level of the navel). This measurement focuses on central adiposity, which is particularly relevant for health risks. Excess abdominal fat is strongly associated with metabolic risks, even when BMI may be in a normal range.

Waist-Hip Ratio

This involves measuring both waist and hip circumference and calculating their ratio. The waist-hip ratio provides information about fat distribution patterns. Higher ratios indicate more fat stored around the abdomen (“apple” shape) which carries greater health risks than fat stored around the hips and thighs (“pear” shape).

These Alternatives Offer Advantages Over BMI by

• Actually measuring fat rather than using weight as a proxy.
• Distinguishing between different types of body fat distribution.
• Potentially providing better prediction of health risks.
• Being more useful for certain populations where BMI has limitations (such as athletes or elderly individuals).

Application in Public Health

BMI can detect overweight and obesity that poses increased health risk. So by identifying the number of people with high BMI (who are otherwise healthy) can educate the people about their health risk and thus allows us to intervene and prevent the condition from becoming worse. This procedure in Public Health practice is called “Screening”

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Mohammad Nazif Uddin is a Marketing and Supply Chain Management student and fitness enthusiast with over 5 years of bodybuilding experience. As the founder of Muscle Theory, he shares practical insights on fitness supplements to help others make informed choices and achieve their goals safely.