BMI Calculator: Calculate Your BMI


BMI Calculator

It is an excellent tool to measure a person’s leanness or fatness as per height and weight. It widely describes whether your are in healthy zone or need to lose or gain weight. BMI ranges may vary based on your exercise regime. More you gain weight more will be the BMI but it does not mean that you are obese it can be because of high muscle mass also.

Body Measurement

What Is Body Mass Index?

BMI is Body Mass Index a parameter to assess nutritional status as per height and weight. It is a ratio between weight in kilograms and height in square meters (1).

BMI Index

BMI chart Adults

Standard BMI ranges and nutritional status as per WHO

BMIWEIGHT STATUS
Below 18.5Underweight
18.5 – 24.9Normal weight
25.0–29.9Pre-obesity
30.0–34.9Obesity class I
35.0–39.9Obesity class II
Above 40Obesity class III

BMI chart Kids

BMI for age percentile is basically designed to assess growth pattern of children and teenage

WEIGHT STATUS CATEGORYPERCENTILE RANGE
UnderweightLess than the 5th percentile
Normal or Healthy Weight5th percentile to less than the 85th percentile
Overweight85th to less than the 95th percentile
ObeseEqual to or greater than the 95th percentile

How to calculate body mass index?

In Metric Scale

Step 1: Measure your weight in kg preferably in an empty stomach to get actual weight.

Step 2: Measure height by Stadiometer and convert it to meter by dividing it by 100.

In Imperial Scale

Step 1: Measure weight in pounds by digital weighing machine.

Step 2: Multiply height in inches inself.

Step 3: Divide weight and height, results should be multiplied by 703.

Metric BMI Formula:

BMI = Weight (kg) ÷ Height 2 (meter 2 )

Imperial BMI Formula:

BMI = Weight (lb) ÷ height 2 (in 2 ) × 703

BMI introduction

BMI is a measurement of a person's leanness or corpulence based on their height and weight, and is intended to quantify tissue mass. It is widely used as a general indicator of whether a person has a healthy body weight for their height. Specifically, the value obtained from the calculation of BMI is used to categorize whether a person is underweight, normal weight, overweight, or obese depending on what range the value falls between. These ranges of BMI vary based on factors such as region and age, and are sometimes further divided into subcategories such as severely underweight or very severely obese. Being overweight or underweight can have significant health effects, so while BMI is an imperfect measure of healthy body weight, it is a useful indicator of whether any additional testing or action is required. Refer to the table below to see the different categories based on BMI that is used by the calculator.

BMI table for adults
This is the World Health Organization's (WHO) recommended body weight based on BMI values for adults. It is used for both men and women, age 18 or older.

CategoryBMI range - kg/m2
Severe Thinness< 16
Moderate Thinness16 - 17
Mild Thinness17 - 18.5
Normal18.5 - 25
Overweight25 - 30
Obese Class I30 - 35
Obese Class II35 - 40
Obese Class III> 40

BMI chart for adults

This is a graph of BMI categories based on the World Health Organization data. The dashed lines represent subdivisions within a major categorization.

BMI table for children and teens, age 2-20

The Centers for Disease Control and Prevention (CDC) recommends BMI categorization for children and teens between age 2 and 20.

CategoryPercentile Range
Underweight<5%
Healthy weight5% - 85%
At risk of overweight85% - 95%
Overweight>95%

BMI chart for children and teens, age 2-20

The Centers for Disease Control and Prevention (CDC) BMI-for-age percentiles growth charts.

Risks associated with being overweight

Being overweight increases the risk of a number of serious diseases and health conditions. Below is a list of said risks, according to the Centers for Disease Control and Prevention (CDC):

  • High blood pressure
  • Higher levels of LDL cholesterol, which is widely considered "bad cholesterol," lower levels of HDL cholesterol, considered to be good cholesterol in moderation, and high levels of triglycerides
  • Type II diabetes
  • Coronary heart disease
  • Stroke
  • Gallbladder disease
  • Osteoarthritis, a type of joint disease caused by breakdown of joint cartilage
  • Sleep apnea and breathing problems
  • Certain cancers (endometrial, breast, colon, kidney, gallbladder, liver)
  • Low quality of life
  • Mental illnesses such as clinical depression, anxiety, and others
  • Body pains and difficulty with certain physical functions
  • Generally, an increased risk of mortality compared to those with a healthy BMI

As can be seen from the list above, there are numerous negative, in some cases fatal, outcomes that may result from being overweight. Generally, a person should try to maintain a BMI below 25 kg/m2, but ideally should consult their doctor to determine whether or not they need to make any changes to their lifestyle in order to be healthier.


Limitations of BMI

Although BMI is a widely used and useful indicator of healthy body weight, it does have its limitations. BMI is only an estimate that cannot take body composition into account. Due to a wide variety of body types as well as distribution of muscle, bone mass, and fat, BMI should be considered along with other measurements rather than being used as the sole method for determining a person's healthy body weight.

In adults:

BMI cannot be fully accurate because it is a measure of excess body weight, rather than excess body fat. BMI is further influenced by factors such as age, sex, ethnicity, muscle mass, and body fat, and activity level, among others. For example, an older person who is considered a healthy weight, but is completely inactive in their daily life may have significant amounts of excess body fat even though they are not heavy. This would be considered unhealthy, while a younger person with higher muscle composition of the same BMI would be considered healthy. In athletes, particularly bodybuilders who would be considered overweight due to muscle being heavier than fat, it is entirely possible that they are actually at a healthy weight for their body composition. Generally, according to the CDC:

  • Older adults tend to have more body fat than younger adults with the same BMI.
  • Women tend to have more body fat than men for an equivalent BMI.
  • Muscular individuals and highly trained athletes may have higher BMIs due to large muscle mass.

In children and adolescents:

The same factors that limit the efficacy of BMI for adults can also apply to children and adolescents. Additionally, height and level of sexual maturation can influence BMI and body fat among children. BMI is a better indicator of excess body fat for obese children than it is for overweight children, whose BMI could be a result of increased levels of either fat or fat-free mass (all body components except for fat, which includes water, organs, muscle, etc.). In thin children, the difference in BMI can also be due to fat-free mass.

That being said, BMI is fairly indicative of body fat for 90-95% of the population, and can effectively be used along with other measures to help determine an individual's healthy body weight.

BMI formula

Below are the equations used for calculating BMI in the International System of Units (SI) and the US customary system (USC) using a 5'10", 160-pound individual as an example:

USC Units:
BMI = 703 × 
mass (lbs)
height2 (in)
= 703 × 
160
702
= 22.96 
kg
m2
SI, Metric Units:
BMI = 
mass (kg)
height2 (m)
 = 
72.57
1.782
 = 22.90
kg
m2

Ponderal Index

The Ponderal Index (PI) is similar to BMI in that it measures the leanness or corpulence of a person based on their height and weight. The main difference between the PI and BMI is the cubing rather than squaring of the height in the formula (provided below). While BMI can be a useful tool when considering large populations, it is not reliable for determining leanness or corpulence in individuals. Although the PI suffers from similar considerations, the PI is more reliable for use with very tall or short individuals, while BMI tends to record uncharacteristically high or low body fat levels for those on the extreme ends of the height and weight spectrum. Below is the equation for computing the PI of an individual using USC, again using a 5'10", 160-pound individual as an example:

USC Units:
PI = 
height (in)
mass (lbs)
 = 
70
160
 = 12.89
in
lbs
SI, Metric Units:
PI = 
mass (kg)
height3 (m)
 = 
72.57
1.783
 = 12.87
kg
m3



Risks of being overweight?

Overweight or severely obesity increases the risk of many diseases as per Postgraduate Medicine review studies :

  • Diabetes
  • Cardiovascular disorders
  • Metabolic Syndrome
  • High Blood Pressure
  • Pancreatitis
  • Gallbladder diseases
  • Sleep Apnea and breathing problem
  • Osteoarthritis
  • Non Alcoholic Fatty Liver diseases
  • Pulmonary Complications
  • Depression
  • Low Quality of life

Risks for being underweight?

Being underweight multiple risks are associated with it:

  • Malnutrition
  • Low Bone Mineral Density
  • Poor Immune System
  • Retarded or stunted growth and development among children.
  • Hormonal imbalance especially among women

Limitations of BMI

BMI is not an accurate measure when it comes to analyse body fat

  • BMI measures overall nutritional status in relation to height and weight. No mention of body fat percentage or muscle mass.
  • It does not distinguish water weight, bone mass etc.
  • It is not specific to sex of a person. For eg: BMI of male and female is same whereas male has more muscle mass and female has more of fat mass which is not mentioned in BMI chart

What is a healthy BMI for women?

BMI varies as per age, height and weight. It is invariable in respect to gender. Though women have more fat mass compared to men but it does not affect BMI and no scientific evidence mentioned specific BMI for women.


FREQUENTLY ASKED QUESTIONS (FAQs)

How to use BMI calculator?

  • To calculate your BMI, follow these steps:
  • Enter your weight and select its unit (kilograms or pounds).
  • Enter your height in feet and inches.
  • Press calculate.
  • If you want to calculate again, simply press re-calculate.

How is BMI calculated?

BMI is calculated by dividing a person’s weight in kilograms by the square of his/her height in meters. For example, if your weight is 60 kilograms and your height is 5 feet 3 inches, your BMI will be calculated as follows:60 / 2.61 (1.6 * 1.6) (5 feet 3 inches is approximately 1.6 meters)This gives us a BMI reading at 22.9.

Why is BMI calculation important for your health?

The National Institute of Health (NIH) has now defined BMI to be the deciding parameter to know if you are underweight, normal weight, overweight or obese. If you do not fall in the category of normal weight, your health is at risk. Let’s say your BMI is 17.5. This means that you are underweight. Being underweight makes you more prone to diseases because it signifies that your body’s immunity is weak. You can even get osteoporosis in later stages of life or be anaemic. However, if you are overweight, obese or severely obese, your chances of developing various diseases increase with the increase in your BMI number. You get more prone to diseases such as high blood pressure, type 2 diabetes, high cholesterol, coronary artery disease, stroke, among many others.

What is the average BMI value for children and adults?

In children, BMI is calculated in the same way as adults but the healthy and unhealthy ranges are determined in a different way. We do not have fixed values to determine healthy and at-risk thresholds in children. Children’s BMI values are compared with other children of the same age and sex and a percentile is calculated.If the BMI value is below the 5th percentile for children, they are considered underweight. If the BMI value is over 95th percentile value, they are considered obese. A value within 85th and 95th percentile is considered overweight and from 5th to 85th percentile, the value is considered as normal.

When to see a doctor?

Ideally, if your BMI belongs to any category other than normal, you should get yourself tested every once in six months or a year at the maximum. However, the farther your BMI is from the normal range, that is 18.5 to 25, the more risk you are at. If you are severely underweight or even at the beginning threshold of obesity, you must see a doctor immediately. For the rest of the readings, it is difficult to tell the exact condition of your health because of the limiting extent of a BMI number. The above value only gives you an estimate that applies to everyone. They are non-personal and should not replace medical advice in any situation.