Smart BMI Calculator


What is BMI?

Body mass index (BMI) is a number calculated from a person’s weight and height. The BMI is defined as the body mass divided by body height squared and is universally stated in kg/m2 units, coming from mass in kilograms and height in meters.

A table[note 1] or chart that presents BMI as a function of mass and height using contour lines or colors for different BMI categories and may utilize other units of measurement that can be used to calculate BMI (converted to metric units for the calculation).

Based on tissue mass (muscle, fat, and bone) and height, the BMI is a simple rule of thumb used to classify a person as underweight, normal weight, overweight, or obese. That categorization is the subject of significant controversy about where the dividing lines between groups should be placed on the BMI scale. Underweight (less than 18.5 kg/m2), normal weight (18.5 to 25), overweight (25 to 30), and obese are the commonly accepted BMI categories (over 30).


What is the formula for calculating BMI?

The BMI is a straightforward calculation based on a person’s height and weight. BMI = kg/m2, where kg represents a person’s weight in kilograms and m2 represents their height in meters squared.

  • Metric units: BMI = weight (kg) ÷ height2 (meters)
BMi calculating formula with apple
  • US units: BMI = (weight (lb) ÷ height2) * 703 (inches)


The BMI is commonly used to determine how far a person’s body weight deviates from what is considered normal or acceptable for their height. Body fat (adipose tissue) may account for some of the weight gain or loss, but other characteristics such as muscularity have a substantial impact on BMI (see discussion below and overweight). 

A BMI of less than 18.5 is considered underweight by the WHO and may suggest malnutrition, an eating disorder, or other health issues, whereas a BMI of 25 or more is considered overweight, and a BMI of greater than 30 is considered obese.

These BMI ranges are solely useful as statistical classifications.

BMI CategoryBMI Range
Health risk
Underweight18.4 and belowMalnutrition risk
Normal weight18.5 – 24.9Low risk
Overweight25 – 29.9Enhanced risk
Moderately obese30 – 34.9Medium risk
Severely obese35 – 39.9High risk
Very severely obese40 and aboveVery high risk

BMI Chart

BMI Chart

BMI Chart Teenage and Children (aged 2 to 20)

For youngsters, BMI is employed in a different way. Calculated in the same manner as for adults but in comparison to other children of the same age. The BMI is compared to the percentiles of children of the same sex and age, rather than predefined limits for underweight and overweight.

Underweight people have a BMI below the 5th percentile, while obese people have a BMI over the 95th percentile. Overweight children have a BMI between the 85th and 95th percentiles.

BMI Chart for Boys

BMI Chart for Girls

Why Use This Test?

  • Free. This free online Smart BMI Calculator will help you determine if you are underweight, normal weight, overweight, or obese, according to the World Health Organization’s (WHO) classification, which was improved by Bachmann, Fäh, and von Grünningen.
  • Based on peer-reviewed research. The current results and charts of this Smart BMI Test are based on adjusted values published in peer-reviewed research and journals.
  • Improved measure of the WHO BMI. For many years, the WHO’s BMI measurement has been slammed. Some of these criticisms will be addressed by Smart BMI.
  • Statistical controls. The current test’s user results are entered into an anonymous database, and statistical analyses are run to guarantee that the results are as valid and reliable as possible.

Who shouldn’t use a BMI calculator?

Muscle builders, long-distance runners, pregnant women, the elderly, and young children are not eligible for BMI. This is because BMI only considers the number, not whether the weight is carried as muscle or fat. Those with more muscle mass, such as athletes, may have a higher BMI but are not at greater risk of developing health problems. A lower BMI is associated with those who have less muscle mass, such as children who have not completed their growth or the elderly who are losing muscle mass. Because a woman’s body composition changes throughout pregnancy and lactation, BMI is ineffective.

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