BMI Calculator

BMI (Body Mass Index) is a number calculated from a person’s weight and height. BMI is a fairly reliable indicator of body fatness for most people. Additionally, BMI is an inexpensive and easy-to-perform method of screening for weight categories that may lead to health problems.

BMI Calculator

BMI Calculator


What is BMI?

BMI stands for "Body Mass Index." It's a numerical value calculated using a person's weight and height. The BMI is used as a basic indicator of whether a person's weight is within a healthy range for their height. It's commonly used by healthcare professionals as a simple way to assess whether someone is underweight, normal weight, overweight, or obese. However, it's important to note that BMI doesn't consider factors like muscle mass or body composition, so it has limitations in certain cases. It's just one of many tools used to evaluate overall health.

You can then use an online BMI calculator to check your BMI, which will help you understand if you’re underweight, a healthy weight, overweight or obese. Or, you can measure your height in metres and weight in kilograms. Divide your weight by your height squared to calculate your BMI.

Underweight – BMI less than 18.5
Normal weight – BMI between 18.5 and 24
Overweight – BMI between 25 and 29.9
Obese – BMI above 30

Is BMI Reliable?

The reliability of BMI depends on the context in which it's used. BMI can be a useful and convenient tool for quickly assessing whether a person's weight might be within a healthy range for their height. It's commonly used in large-scale health studies and screenings due to its simplicity and ease of calculation.

However, BMI has limitations that can affect its reliability in certain cases:

  1. Muscle Mass: BMI doesn't differentiate between muscle and fat. People with high muscle mass may have a higher BMI even though they are not overweight or unhealthy.
  2. Body Composition: BMI doesn't consider where the body fat is located. Central obesity (fat around the abdomen) can be more harmful than fat in other areas.
  3. Age and Gender: BMI doesn't account for differences in body composition that can occur with age and between genders.
  4. Health Conditions: Some health conditions can affect body weight and composition, which can influence the accuracy of BMI assessments.
  5. Ethnicity: BMI classifications may not be equally applicable to all ethnicities and populations.
  6. Pregnancy: BMI is not suitable for pregnant women.
  7. Elderly Population: In older adults, BMI might not be as accurate a measure of health due to changes in muscle mass and bone density.
  8. Athletes: Highly trained athletes with low body fat and high muscle mass might have a higher BMI that doesn't accurately reflect their health.

Given these limitations, while BMI can provide a general indication of weight-related health, it's important to consider other factors and assessments, such as waist circumference, body composition analysis, and overall health markers, for a more comprehensive evaluation. Always consult with a healthcare professional to get a well-rounded understanding of your health status.

BMI Formula

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

In this formula:

  • "weight" is the person's weight in kilograms (kg).
  • "height" is the person's height in meters (m).

To calculate your BMI, divide your weight in kilograms by the square of your height in meters. The resulting number is your BMI. It's important to note that BMI is a simple estimation and has its limitations, as discussed earlier. Always seek professional medical advice for a comprehensive assessment of your health.

Limitations of an Online BMI Calculator

Here are some limitations of using an online BMI calculator:

  1. Lack of Context: Online calculators only use height and weight to calculate BMI, without considering other factors such as age, gender, body composition, muscle mass, and health conditions. These factors can significantly affect the accuracy of BMI as an indicator of health.
  2. Muscle Mass: BMI doesn't differentiate between muscle and fat. Individuals with high muscle mass may be classified as overweight or obese even if they are in good health.
  3. Body Composition: BMI doesn't account for where fat is located in the body. Central obesity (fat around the abdomen) can pose greater health risks than fat in other areas.
  4. Ethnic and Gender Differences: Different ethnicities and genders can have varying distributions of muscle and fat, making a single BMI threshold less applicable to all groups.
  5. Age Considerations: BMI might not accurately reflect health in children, adolescents, and older adults due to changing growth patterns, bone density, and muscle mass.
  6. Pregnancy: BMI isn't suitable for pregnant individuals, as it doesn't consider the changes in body composition during pregnancy.
  7. Health Conditions: Certain medical conditions and medications can influence weight and body composition, affecting the reliability of BMI calculations.
  8. Accuracy of Input Data: Errors or inaccuracies in entering weight or height can lead to incorrect BMI calculations.
  9. Individual Variation: Health is complex and varies from person to person. Relying solely on BMI might overlook important individual health markers.
  10. Overall Health Assessment: BMI doesn't capture the full picture of health. It doesn't account for cardiovascular fitness, blood pressure, cholesterol levels, and other important indicators.
  11. Psychological Impact: Relying on BMI alone might contribute to body image issues or unhealthy attitudes toward weight.
  12. Lack of Medical Context: Online calculators lack the ability to provide personalized medical context and recommendations based on the calculated BMI.

While online BMI calculators can offer a quick estimate, they should be used cautiously and not as a definitive measure of health. For a comprehensive understanding of your health, consult with a healthcare professional who can consider all relevant factors.


1. What is BMI? Body Mass Index (BMI) is a numerical value derived from a person's weight and height. It's used to categorize individuals into different weight-related health categories.

2. How is BMI calculated? BMI is calculated using the formula: BMI = weight(kg) / (height(m))^2. The resulting value indicates where the individual falls on the BMI scale.

3. What do the different BMI categories mean? BMI categories include underweight, normal weight, overweight, and various levels of obesity. These categories help assess whether a person's weight is within a healthy range for their height.

4. Is BMI an accurate indicator of health? While BMI provides a general estimation of weight-related health, it doesn't consider factors like muscle mass, body composition, and distribution of fat. It may not be accurate for individuals with higher muscle mass or certain health conditions.

5. Can BMI be different for athletes and active individuals? Yes, individuals with higher muscle mass may have a higher BMI, classifying them as overweight or obese. This is a limitation of using BMI for very active or athletic individuals.

6. Does BMI vary by age? Yes, BMI values may vary in children, adolescents, and the elderly due to growth patterns, bone density changes, and other factors.

7. Is BMI suitable for all ethnicities and populations? BMI thresholds may not apply equally to all ethnicities, as different populations have varying body compositions and health risks.

8. Can BMI be used during pregnancy? BMI isn't suitable for pregnant individuals, as it doesn't account for the changes in body composition and weight distribution that occur during pregnancy.

9. Should I solely rely on BMI to assess my health? No, BMI is just one aspect of health assessment. It's important to consider other factors like diet, exercise, body composition, medical history, and overall well-being.

10. How can I improve my BMI if it's in an unhealthy range? Focus on adopting a balanced diet and a regular exercise routine. Consult a healthcare professional for personalized guidance on improving your health.

11. Can BMI predict health risks? While high BMI can indicate potential health risks, it's not a guarantee. Health risks are influenced by various factors beyond weight.

12. Should I consult a doctor about my BMI? If you're concerned about your weight or health, it's a good idea to consult a healthcare professional. They can provide personalized advice based on a comprehensive assessment.

13. Are online BMI calculators accurate? Online calculators provide a rough estimate, but accuracy depends on the quality of input data and the calculator's design. They don't replace professional medical advice.

14. What other measurements are important for assessing health? Waist circumference, body fat percentage, blood pressure, cholesterol levels, and overall fitness are additional measurements that provide a more complete picture of health.

Remember, while BMI can offer a general idea of weight-related health, it's important to consider it alongside other health indicators and consult a healthcare professional for a comprehensive assessment.