How to Calculate Body Mass Index (BMI)

Kickstart your wellness journey with the BMI calculator.
To work with the BMI calculator, all you need is your weight and height. It's a basic division - weight divided by the square of height.

In the face of a mounting obesity crisis, the BMI calculator has emerged as a crucial population measurement tool. It assesses the connection between your weight and fat, aiding in identifying excess body fat and unraveling the health hazards that come with the extra weight.

However, take note: the BMI calculator isn't flawless - it can overestimate for those with a muscular frame and underestimate for the athletically inclined.

Calculate BMI
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BMI calculator may overestimate and underestimate for muscular body mass and athletic body respectively.

BMI, Ideal Body Weight and Obesity

Ideal Weight range as BMI

– BMI between 18.5 and 24.9

Overweight

- BMI between 25 and 29.9

Class 1 Obesity

- BMI of 30 but less than 35

Class 2 Obesity

- BMI of 35 but less than 40

Class 3 or severe obesity

- BMI of 40 or higher

What is BMI?

BMI is defined as the proportion of a person's weight in kilograms (or pounds) divided by their height in meters (or feet). The presence of a high body mass index is indicative of a high level of body fat. An individual's BMI is used to identify weight categories that may pose a health risk; however, it does not diagnose his or her body fatness or health(1^✔).

BMI formula

For both adults and children, the BMI is calculated according to the formula below:

BMI in kilograms and meters: weight (kg) / [height (m)]²
BMI in pounds and inches: weight (lb) / [height (in)]² x 703(2^✔)

Normal BMI

Body Mass Index (BMI) is a widely used indicator of healthy weight. It is a measure of body fat based on a person's height and weight. Here are the normal BMI ranges for men, women, teens, and children:

For men, women, and teens (ages 13-19):

Normal BMI range: 18.5-24.9
BMI below 18.5 is considered underweight
BMI above 24.9 is considered overweight(3^✔)

For children (ages 2-12):

A child's BMI is evaluated based on their age and gender using a percentile chart. A BMI percentile between 5th and 85th is considered healthy, between 85th and 95th is considered overweight, and above 95th is considered obese.

These normal BMI ranges are based on guidelines from the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO)(4^✔).

The National Institute of Health (NIH) and the Centers for Disease Control and Prevention (CDC) both recommend using BMI as a screening tool for overweight and obesity. The World Health Organization (WHO) also uses BMI as a measure of obesity in adults.

However, the CDC also notes that BMI is not a diagnostic tool and that other factors, such as waist circumference and overall health, should be considered when assessing an individual's weight status.

The NIH also notes that BMI may not accurately reflect body fat in athletes and those with a muscular build(5^✔).

BMI can be applied to both men and women. It is advisable to use ‘Body Mass Index’ along with ‘Waist to Hip Ratio’ to get a complete picture of your weight status.

IMPORTANT NOTE: This BMI calculator is not intended to provide clinical advice. Since BMI is calculated based on weight and height, it serves only as an indication of body fatness, and it is beneficial to consult with a professional for advice on maintaining a healthy weight.

FAQs:

1. What is a healthy BMI range and why is it important to stay within this range?

The BMI range for a healthy individual is between 18.5 and 24.9. Staying within this range can reduce the risk of developing many health problems such as heart disease, diabetes, and high blood pressure. It is important to maintain a healthy BMI range through healthy lifestyle choices such as exercise and a balanced diet(6^✔).

2. Can BMI accurately predict health risks and conditions?

BMI is a useful tool to help identify potential health risks and conditions. However, it is not always accurate as it does not take into account factors such as muscle mass, bone density, and body composition. Therefore, it is important to use BMI in conjunction with other health metrics to create a comprehensive health plan(7^✔).

3. How do age, gender, and ethnicity impact BMI?

Age, gender, and ethnicity can impact BMI as they can affect body composition and metabolism. For example, older adults may have more body fat and less muscle mass, resulting in a higher BMI. Additionally, certain ethnic groups may have a higher or lower BMI range due to differences in body composition(8^✔).

4. How do lifestyle factors, such as diet and exercise, impact BMI and overall health?

Lifestyle factors such as diet and exercise can have a significant impact on BMI and overall health. Eating a balanced diet and engaging in regular physical activity can help maintain a healthy BMI and reduce the risk of many health problems such as heart disease and diabetes(9^✔).

5. How does a higher Body Mass Index (BMI) affect long-term health outcomes?

Obesity is linked to a wide range of serious health conditions, and the risk increases as BMI rises.

A recent study published in NEJM Evidence, involving over 270,000 participants, found that individuals with obesity face a stepwise increase in risk for 16 chronic conditions. These include chronic kidney disease, hypertension, pulmonary embolism, and others. The higher the BMI category (Class I, II, or III), the greater the associated health risk.(10^✔).

6. Which health risks are most strongly linked to severe (Class III) obesity?

Class III obesity (BMI ≥ 40) is most strongly associated with:

Obstructive sleep apnea
Type 2 diabetes
Metabolic dysfunction–associated steatotic liver disease (MASLD)
Even conditions with weaker associations—like asthma or osteoarthritis—still showed twice the risk compared to individuals with normal BMI.

(10^✔).

7. Are there any limitations to using BMI as a measure of body fat?

Yes, BMI has some limitations. For example, it does not take into account the distribution of body fat, which can affect health outcomes. Additionally, BMI may not be accurate for certain populations, such as pregnant women or older adults. It is important to interpret BMI in conjunction with other measures of health, such as waist circumference, blood pressure, and blood lipid levels(5^✔).