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How to Calculate Body Mass Index

Due to the rising obesity rate, people are well concerned about weight management, which involves tracking the weight over time and identifying the correct body weights for various individuals. Understanding and knowing the proper value of the body is essential for an individual’s overall health as obesity causes many chronic illnesses such as hypertension, type 2 diabetes, and heart diseases. Also, check out the top BMI weighing scale to make this process easier.


Weight Management involves the techniques and physiological activities that provide a person with a certain weight. The majority of these techniques include long-term lifestyle strategies, promoting a healthy diet, and regular physical activity. Body Mass Index (BMI) is one such essential component of weight measurement, which gives a general idea about an individual’s overall mass.

What is BMI?

A simple calculation using the height and weight of a person is called Body Mass Index, the formula being BMI= kg/m2, where kg is the weight of a person and m2, the height of the person in square meters.

When a person’s BMI is 25.0, he is overweight because the healthy BMI range is 18.5-24.9. Hence, BMI is an easy and inexpensive screening weight category like underweight, overweight, obesity, and healthy weight.

Process of using BMI

Though being a screening tool, BMI cannot diagnose the body’s fatness or an individual’s health. In measuring BMI, numerous assessments are performed by a healthcare provider, which includes measurements of skinfold thickness, diet evaluations, family history, corporeal activity.

Calculation of BMI

For adults as well as children, BMI is calculated in the same manner. The following are the formulas on which the calculation is based.

Units = Kilograms and meters (or cms), Formulae = weight(kg)/ height(m2)

The Metric System Suggests that the formulae for BMI = Wight in kgs divided by Height in square meters.

For example, Wight = 70 kg, Height =165cm(1.65m). Therefore, BMI= 70/(1.65)2 = 25.7

In the case of Pounds and inches, the formula becomes weight(lb)/[height(in)]2×703.BMI is calculated by dividing weight in pounds(lbs) by height(inches) squared and then by multiplying by a factor of conversion, 703.For example, if weight = 170 lbs, height =3’7″(43″), then:

BMI = [170/(43)2]x703 = 64.63

Interpretation of BMI

Interpretation of BMI differs from one age group to another. Though the formula for BMI calculation remains the same for all age groups yet, the interpretation differs in children, teens, and adults. BMI interpretation for children and teens is somewhat the same, but the adult interpretation differs somewhat. BMI of children and teens are gender-specific, as the quantity of body fat varies among girls and boys. The CDC for age-growth-tables records these accounts of BMI.BMI according to age and their respective percentiles are –

  • < 5th percentile = Underweight.
  • 5th percentile – < 85th percentile = Healthy weight.
  • 85th percentile – < 95th percentile = Overweight.
  • >= 95th percentile = Obese.

In the case of adults, the BMI interpretation does not depend on gender or age. For people aged 20 years or more, BMI is carried out by using categories of standard weight. These categories remain the same irrespective of gender, body types, and ages.

The categories of standard weight with BMI for adults are as follows –

  • Below 18.5: Underweight.
  • 5-24.9: Normal (Healthy) weight.
  • 0- 29.9: Overweight.
  • 0 and above: Obese.

BMI does not differentiate a healthy body from a diseased body or a condition of illness. It is an initial measure of screening for both children, adolescents, and adults. The health care provider interrogates other components into the account of health assessment for providing appropriate health report.

Factors Determining BMI

The prime BMI determining factors is the weight and height of an individual. Yet, there are several other minutes but equally important factors that affect the BMI of a person. Factors like age, gender, physical activity, lifestyle, and mass of muscle also influence the body’s BMI.

BMI does not differentiate between excess fat and muscle. It does not provide information about fat distribution among individuals.

Limitations of BMI usage

BMI doesn’t take into record the weight of the muscle fat. It just carries a number; hence, BMI is not used for muscle builders, athletes, older adults, infants, and pregnant women. Athletes or people with higher mass of muscle might have elevated BMI, but that does not suggest that they are at higher health risk.

Similarly, individuals with a lower mass of muscle might have lower BMI. At the time of pregnancy, the composition of a woman’s body changes; hence, BMI becomes inappropriate.

The Bottom Line 

BMI is a rational indicator that indicates the body fat of both children and adults. BMI does not measure fat of the body, directly and hence, it must not be used as a perfect diagnostic tool. BMI should be used as an alternative in keeping track of the status of weight in populations.

Also, BMI can be used as a screening tool for identifying potential weight complications in individuals. Further researches on BMI is being carried out to understand the BMI correlation in a better way. Just bear in mind that it is nothing more than a metric, and there are other factors to consider as well for carrying out a healthy lifestyle.

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