Body Mass Index: Number Scale Of Your Health

What is Body Mass Index?

Body mass index (BMI) is derived from a person’s mass (weight) and height. BMI is defined as weight divided by height squared and is expressed in units kg/m2 derived from weight in kilograms and height in meters.

BMI can be determined using charts or graphs that show BMI as a function of mass and height, using contour lines or colors for various BMI categories, and can use other units of measurement.

Importance of BMI

BMI is a useful rule of thumb used to roughly classify a person as underweight, normal weight, overweight, or obese based on tissue mass (muscle, fat, bone) and height.

BMI Classifications

Major BMI Classifications are:

  • Underweight -less than 18.5 kg/m2
  • Ideal Weight-18.5 to 24.9 kg/m2
  • OverWeight-25 to 29.9 kg/m2
  • Obese-30 and above kg/m2

BMI <20 and >25 were associated with higher all-cause mortality, with risk increasing away from the 20-25 range.

How is BMI Calculated?

BMI is calculated the same way for adults and children. The calculation is based on the formula:


Measurement Units

Formula and Calculation

Kilograms and Metres or Centimetres Formula : weight(kg)/[height(m)]2

In the metric system, the formula for BMI is your weight in kilograms divided by your height in metres squared. Height is commonly measured in centimetres, so divide the height in centimetres by 100 to get the height in metres.

Example: Weight = 68 kg, Height = 165 cm (1.65 m)

Calculation: 68 ÷ (1.65)2 = 24.98

Pounds and Inches Formula : weight(lb)/[height(in)]2

Calculate your BMI by dividing your weight in pounds (lbs) by the square of your height in inches (inch) and multiplying by a conversion factor of 703.

Example: Weight = 150 lbs, Height = 5’5″ (65″)

Calculation: [150 ÷ (65)2] x 703 = 24.96


BMI for Children and Teens

BMI is calculated using the same formula as adult BMI, but is interpreted differently for children and adolescents. Because the amount of body fat changes with age, and the amount of body fat differs between girls and boys, BMI in children and adolescents should be age- and gender-specific. It explains the differences and visually shows BMI as a percentile ranking. These percentiles were determined using representative data of her 2–19-year-old US population collected in various censuses from 1963–65 to 1988–9411.

Accuracy of BMI


Although the correlation between BMI and body fat percentage is very strong, people with the same BMI may have different body fat percentages.

For the same BMI, women tend to have more body fat than men.

Even with the same BMI, the body fat percentage increases or decreases depending on race / ethnicity.

For the same BMI, on average, older people tend to have more body fat than younger adults.

An athlete has less body fat than a non-athlete with the same BMI.

BMI also appears to be more accurate as an index of body fat in people with higher BMI and body fat scores.

Risks caused by High BMI


BMI ranges are based on the relationship between body weight and illness and mortality. Overweight and obese people are at increased risk of the following diseases:

  1. Coronary artery disease
  2. Dyslipidemia
  3. Type 2 diabetes
  4. Gallbladder disease
  5. Hypertension
  6. Osteoarthritis
  7. Sleep apnea
  8. Stroke

Other ways to measure body fitness

Other methods of measuring body fat percentage include subcutaneous fat thickness measurements (using Vernier calipers), underwater weighing, bioelectrical impedance, dual-energy X-ray absorptiometry (DXA), and isotope dilution are included. However, these methods are not always readily available, are expensive, or require highly skilled personnel. Additionally, many of these methods can be difficult to standardize across observers and machines, making comparisons across studies and time periods difficult.

Surprising myths and facts about BMI

Myth: A low BMI indicates good health

Fact: Having a low BMI does not mean you are healthy. People with low BMI are more susceptible to infections. Being underweight has always been associated with a weak immune system.

Myth: A excessive BMI will increase the chance of a coronary heart attack.:

Fact: Amount of fat is associated with heart problems, but not as much as higher BMI.

Myth: A healthy diet and exercise means a low BMI.

Fact: Despite eating healthy and exercising regularly, maintaining a fit body is very important, which has nothing to do with a low BMI.


Body mass index (BMI) measures the percentage of body fat based on weight for height. A value derived from BMI determines whether a person is underweight, overweight, or healthy, depending on their height. A high BMI is a sign of being overweight, while a low BMI indicates that your body does not have enough fat.It can also be easily measured with our online BMI calculator by simply entering your height and weight.


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