Body Mass Index (BMI) Calculator

BMI Calculator

Gender: Age: Height:

Weight:

Your BMI: []

BMI Classification:
Underweight = <18.5
Normal weight = 18.5–24.9
Overweight = 25–29.9
Obese = BMI of 30 or greater

What is BMI

BMI stands for Body Mass Index, and it measures body fat based on a person’s weight and height.

The BMI is calculated by dividing a person’s weight in kilograms by the square of their height in meters. The result then determines whether the person is underweight, of normal weight, overweight, or obese.

The body mass index is a screening tool used to identify potential health risks associated with a person’s weight. However, it is essential to note that the index is not a perfect measure of health, as it does not account for factors such as body fat, muscle mass, body composition, or overall well-being.

It should be combined with other health assessments to gain a more profound understanding of someone’s overall health and fitness.

Know More: 100+ Safe And Fast Ways To Lose Weight (Backed By Science)

How To Calculate BMI

To calculate your BMI manually, you must determine your weight and height.

Here are the steps to calculate BMI:

1. Measure your weight

You can use a scale to measure your weight in kilograms.

If you don’t have access to a scale that measures kilograms, you can convert your weight from pounds to kilograms by dividing your weight in pounds by 2.205.

2. Measure your height

Use a tape measure or ruler to measure your height in meters.

If you don’t have access to a metric tape measure or ruler, you can convert your height from feet and inches to meters by multiplying your height in feet by 0.3048 and adding your height in inches multiplied by 0.0254.

The BMI formula divides a person’s weight in kilograms by the square of their height in meters.

The Formula for Calculating BMI is

BMI Metric Units formula (kg, cm, m):

BMI = (weight (kg) / height^2 (m^2))

For example, if you weigh 70 kilograms and are 1.75 meters tall, your BMI would be calculated as follows:

BMI = 70 kg / (1.75 m × 1.75 m) BMI = 22.86

Your BMI is 22.86, which is a healthy weight.

BMI Imperial Units formula (Inch and Pound):

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

BMI = 703 x Weight (lbs) / Square of height in inches

For example, if you weigh 150 lbs and are 65 inches tall, your BMI would be calculated as follows:

BMI: [150 ÷ (65)²] x 703 = 24.96
Your BMI is 24.96, which is a healthy weight.

BMI Classifications

The BMI classifications for overweight and obese (Nuttall, 2015).

BMI	Disease Risk	Classification
< 18.5	Increased	Underweight
18.5–24.9	Low	Healthy weight
25.0–29.9	Increased	Overweight
30.0–34.9	High	Obese
35.0–39.9	Very high	Obesity II
≥ 40.0	Extremely high	Obesity III

BMI Categories

The formula for calculating BMI is the same for both men and women, based solely on weight and height.

BMI Chart For Men and Women

The mass index (BMI) is a valuable tool for assessing whether your weight is appropriate for your height. Deviating from the recommended weight range based on height can pose long-term health risks.

Although BMI should not be the sole factor to consider for one’s health and fitness, it is a helpful starting point.

To calculate BMI, you must know their height and weight and compare it with the BMI chart.

BMI Table for Both Males and Females

The resulting number is then compared to BMI categories established by the World Health Organisation (WHO) and other health organisations. These categories include:

Underweight: less than 18.5
Normal weight: 18.5 to 24.9
Overweight: 25 to 29.9
Obese: 30 to 35
Morbid obesity: Over 35

Obesity is frequently subdivided into categories:

Obesity Class 1: BMI of 30 to < 35
Obesity Class 2: BMI of 35 to < 40
Obesity Class 3: BMI of 40 or higher. Class 3 obesity is sometimes categorised as “severe” obesity.

BMI Chart for Children and Teens, age 2-20

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

However, the BMI scale used to interpret the results may differ slightly for males and females. Males tend to have more muscle mass than females, which can affect their body mass index.

BMI Table for Children and Teens, Age 2-20

Using a standard adult BMI chart is inappropriate, as a child’s body undergoes rapid development and changes throughout childhood. Instead, doctors use a specific chart to monitor whether a child’s weight is appropriate for their height.

To determine this, doctors calculate the child’s BMI using their height and weight. The resulting BMI value is then compared to other children of the same age and gender using percentages and percentiles. Weight categories for children are established based on these percentiles, including:

For example, a 25th percentile BMI for a 6-year-old female child would indicate that the child's weight is higher than 25% of girls aged 6.

The Centres for Disease Control and Prevention (CDC) recommends categorising children and teens between the ages of 2 and 20 by BMI.

Category	Percentile Range
Underweight	<5%
Healthy weight	5% – 85%
At risk of overweight	85% – 95%
Overweight	>95%

How to Calculate BMI for Athletes

Calculating BMI for athletes is the same as for non-athletes. However, because athletes or bodybuilders tend to have higher levels of muscle mass, which weighs more than fat, BMI may not accurately measure their body fat.

Other methods, such as skinfold measurements or bioelectrical impedance analysis, may be more appropriate in such cases.

Athletes should consult a healthcare professional or sports nutritionist who can assess their bodies and provide personalised recommendations.

BMI Calculator For Seniors

A body mass index can be used as a screening tool for seniors, but it may not be the most accurate measure of body fat for older adults.

This is because older adults may experience changes in their body composition, such as a decrease in muscle mass and an increase in body fat, which can impact BMI values.

The same formula is used to calculate BMI for seniors as for other adults: weight in kilograms divided by height in square meters. However, the results may be interpreted differently.

According to the World Health Organisation, a BMI value of 18.5-24.9 is considered a healthy weight range for adults aged 18–65, but a slightly higher BMI may be more appropriate for seniors.

Seniors should consult a healthcare provider or a registered dietitian, who can provide personalised advice based on their individual needs and health status.

Importance and Benefits of Measuring BMI

The Body Mass Index (BMI) is a crucial measure of body fat that provides a quick and easy way to screen for potential health risks associated with weight.

Here are some reasons why BMI is important:

1. Assessing Health Risks

A BMI is a helpful tool for identifying who is at increased risk for health problems related to their weight, such as type 2 diabetes, heart disease, high blood pressure, and certain types of cancer.

Research has shown that people with higher BMI have an increased risk of these health concerns.

2. Simple Screening Tool

A quick and easy screening tool that healthcare professionals can use to identify who may need further evaluation or treatment for weight-related health issues.

3. Motivation for Lifestyle Changes

BMI can be a motivator for people who are overweight or obese to make lifestyle changes to improve their health.

Having a healthy body mass index can help you achieve a healthier weight and reduce your risk of weight-related health concerns.

4. Widely Recognised

BMI is a measure of body fat that doctors and researchers worldwide use to assess body composition.

This universal recognition makes it easy to compare results across different groups and studies.

5. Free of Cost

Compared to pricier and invasive measures of body composition, such as dual-energy X-ray absorptiometry (DEXA) scans, BMI is a cost-effective option for assessing body fat.

Limitations of BMI

Understanding the benefits and limitations of body mass index (BMI) can help you take steps to improve your health and reduce your risk of weight-related health problems.

There are several limitations to consider, including:

BMI does not consider differences in body composition, such as muscle mass.
It does not distinguish between different types of body fat, such as subcutaneous fat and visceral fat.
The body mass index may not accurately measure body fat in older adults, men, and women of different ages, or individuals of other ethnicities.
The body mass index doesn’t consider an individual’s overall health status or other risk factors for weight-related health problems, such as diabetes or heart disease.

Health Risks Related To Being Overweight (High BMI)

Being overweight can increase the risk of developing several health problems, including:

Fat accumulation makes it difficult for the body to utilise insulin properly. It is associated with high blood sugar levels and an increased risk of developing type 2 diabetes.
Being overweight can increase the workload on the heart and blood vessels. It increases high blood pressure and increases the risk of heart disease and stroke.
Excess body fat can increase blood levels of cholesterol and triglycerides. The buildup of plaque in the arteries increases the risk of heart disease.
Excessive body fat can increase the risk of developing blood clots, which can lead to a stroke.
Body fat accumulation can make breathing difficult during sleep, leading to sleep apnea and other sleep-related concerns.
Extra weight stresses the joints, leading to joint pain and an increased risk of getting arthritis.
Fat accumulation in the liver can lead to fatty liver disease and an increased risk of liver damage.
Increase your risk of getting gallstones or other gallbladder problems.
The risk of developing kidney disease and other kidney issues is increased.
Infertility and polycystic ovary syndrome can be caused by excess body fat, which can affect hormone levels and lead to reproductive problems.
Obesity can cause feelings of low self-esteem, depression, and anxiety.
Excess body fat can make breathing more difficult and increase the risk of respiratory issues, including asthma and shortness of breath.
Increase the risk of developing acid reflux, heartburn, and other digestive issues.

Health Risks Related To Being Overweight

The Risks of Being Underweight (Low BMI)

Being underweight can also increase the risk of several health problems, including:

Being underweight can indicate malnutrition, resulting in deficiencies in essential nutrients, including protein, vitamins, and minerals.
Malnutrition can weaken the immune system, making it difficult for the body to fight off infections and illnesses.
Malnutrition can lead to a deficiency of iron and other essential nutrients required for the production of red blood cells, resulting in anaemia and its associated symptoms.
A low BMI can increase the risk of getting osteoporosis and other bone-related issues because a low body weight can lead to a loss of bone density.
Being underweight can affect hormone levels and lead to reproductive issues, including irregular periods and infertility.
Being underweight can hurt growth and development, especially in children and adolescents.

Maintaining a healthy weight through a balanced diet and regular exercise can reduce these health risks.

References

Nuttall FQ. Body Mass Index: Obesity, BMI, and Health: A Critical Review. Nutr Today. 2015 May;50(3):117-128. doi: 10.1097/NT.0000000000000092. Epub 2015 Apr 7. PMID: 27340299; PMCID: PMC4890841.
Khanna D, Peltzer C, Kahar P, Parmar MS. Body Mass Index (BMI): A Screening Tool Analysis. Cureus. 2022 Feb 11;14(2):e22119. doi: 10.7759/cureus.22119. PMID: 35308730; PMCID: PMC8920809.
Nuttall, Frank Q. MD, PhD. Body Mass Index: Obesity, BMI, and Health. Nutrition Today 50(3):p 117-128, May/June 2015. | DOI: 10.1097/NT.0000000000000092
https://www.cdc.gov/obesity/downloads/bmiforpactitioners.pdf
Katherine M. Flegal, Brian K. Kit, Barry I. Graubard, Body Mass Index Categories in Observational Studies of Weight and Risk of Death, American Journal of Epidemiology, Volume 180, Issue 3, 1 August 2014, Pages 288–296.
Edwards, C.H., Aas, E. & Kinge, J.M. Body mass index and lifetime healthcare utilization. BMC Health Serv Res 19, 696 (2019). https://doi.org/10.1186/s12913-019-4577-0

Manish Kumar

Manish is a NASM-certified fitness and nutrition coach with over 10 years of experience in weight lifting and fat loss fitness coaching. He specializes in gym-based training and has a lot of knowledge about exercise, lifting technique, biomechanics, and more.

Through “Fit Life Regime,” he generously shares the insights he’s gained over a decade in the field. His goal is to equip others with the knowledge to start their own fitness journey.