HOW DO YOU CALCULATE BMI?

Body mass index (BMI) is a measure of body fat based on height and weight that applies to adult men and women. It's commonly used to determine whether a person is underweight, normal weight, overweight or obese. Calculating BMI is a simple way to determine whether a person is at an appropriate weight for their height and can be a useful tool for healthcare professionals to assess the health risks associated with being underweight or overweight.

Click here to try our free online BMI calculator.

BMI is calculated by dividing a person's weight by their height squared. The resulting number is then compared to a set of standardized categories to determine a person's weight status. For adults, a BMI below 18.5 is considered underweight, a BMI between 18.5 and 24.9 is considered healthy, a BMI between 25 and 29.9 is considered overweight and a BMI of 30 or above is considered obese.

How To Calculate BMI

To calculate BMI, you'll need to know your weight and height. Weight can be measured in pounds (lbs) or kilograms (kg) and height can be measured in inches (in) or meters (m). To calculate BMI, you can use either of the following formulas:

Imperial Formula

To calculate with pounds and inches:
BMI = weight (lb) / [height (in)]² x 703

Metric Formula

To calculate with kilograms and meters:
BMI = weight (kg) / [height (m)]²

For example, if you weigh 68 kilograms and are 1.7 meters tall, your BMI would be calculated as follows:
BMI = 68 / (1.7²) = 23.5

BMI Calculators

The easiest way to calculate your BMI is to use an online BMI calculator or a smartphone app to calculate your BMI. For example, you can find our free online BMI Calculator here. These tools will typically ask you to enter your weight and height and will then calculate your BMI for you.

BMI calculators are widely available online and can be found on many websites including those of government agencies and health organizations. Some calculators allow users to enter their height and weight in imperial units (inches and pounds), while others require metric units (centimeters and kilograms). Our calculator allows you to use either imperial or metric measurements.

To use a BMI calculator, a person simply enters their height and weight and clicks on a button to calculate their BMI. The calculator then displays the resulting BMI and the corresponding weight category. Some calculators also provide additional information, such as the recommended range of BMI for a person's age and gender or tips for maintaining a healthy weight.

BMI calculators can be a useful tool for individuals who are interested in monitoring their weight and ensuring that they are at a healthy level. However, it's important to note that BMI is not a perfect measure of body fat and can be misleading in certain situations. For example, BMI does not take into account factors such as muscle mass, bone density and distribution of body fat, which can affect a person's weight and health.

Despite these limitations, BMI calculators can still be a useful tool for monitoring weight and promoting healthy habits. It's important to use BMI calculators in conjunction with other measures of body fat, such as skinfold thickness or waist circumference, and to consult with a healthcare provider for a more accurate assessment of weight and health.

BMI Results

Once you have calculated your BMI, you can use it to work out your BMI category and weight status. The World Health Organization (WHO) has established the following BMI classification categories:

1. Underweight: A BMI of less than 18.5 is considered underweight. This may indicate that an individual is not getting enough nutrients or may be suffering from an underlying health condition.
2. Normal weight: A BMI of 18.5 to 24.9 is considered normal weight. This is generally considered a healthy weight range and is associated with a lower risk of developing certain health conditions, such as heart disease and diabetes.
3. Overweight: A BMI of 25 to 29.9 is considered overweight. This may increase an individual's risk of developing certain health conditions, such as heart disease, diabetes and high blood pressure.
4. Obese: A BMI of 30 or higher is considered obese. This increases an individual's risk of developing serious health conditions, such as heart disease, diabetes and high blood pressure.

It's important to note that BMI categories are not the same for everyone and can vary based on factors such as age, gender and ethnicity. For example, older adults may have a higher percentage of body fat but a lower BMI due to age-related muscle loss. Similarly, athletes and bodybuilders may have a high BMI due to their high muscle mass but still be considered healthy.

As a result, BMI is not a perfect measure of body fat as it does not take into account factors such as muscle mass or bone density. For example, a person who is heavily muscled may have a higher BMI due to their muscle mass, even though they may have a low body fat percentage. Similarly, a person with a low BMI may have a higher body fat percentage due to a lack of muscle mass.

BMI can be useful as a general guide but it's not a substitute for more accurate measures of body fat such as skinfold thickness measurements, bioelectrical impedance or dual energy x-ray absorptiometry (DXA).

Benefits Of Knowing Your BMI

There are many reasons why it's important to know your BMI:

1. Assess your weight status: BMI can help you determine if you're underweight, normal weight, overweight or obese. This information can help you make decisions about your diet and physical activity habits to maintain a healthy weight.
2. Assess your risk for chronic diseases: Being overweight or obese can increase your risk for chronic diseases such as type 2 diabetes, heart disease and certain cancers. Calculating your BMI can help you determine if you're at an increased risk for these conditions and take steps to prevent them.
3. Monitor your weight over time: Regularly calculating your BMI can help you track your weight changes over time. This can be especially useful if you're trying to lose weight or maintain a healthy weight.
4. Set weight loss goals: If you're trying to lose weight, calculating your BMI can help you set realistic weight loss goals. For example, if your BMI is in the obese range, it may be more realistic to aim for a 5-10% weight loss rather than trying to lose a large amount of weight in a short period of time.
5. Evaluate the effectiveness of weight loss efforts: Calculating your BMI before and after a weight loss program can help you determine if your efforts are effective. If your BMI has decreased, it may indicate that you have successfully lost body fat.

Why It's Important To Use Waist Measurements With BMI

While BMI can be a useful tool for identifying general trends in population-level weight and health, it has limitations when it comes to assessing an individual's body composition.

As discussed previously, one major limitation of BMI is that it does not take into account differences in body shape or distribution of body fat. For example, two individuals who have the same BMI may have very different amounts of body fat and muscle mass. This is because BMI does not distinguish between fat and lean mass, meaning that it's possible for an individual with a high amount of muscle mass to have a higher BMI even though they may be healthy.

In contrast, waist measurement provides valuable information about the distribution of body fat, specifically abdominal fat. Abdominal fat, also known as visceral fat, is the fat that surrounds the internal organs in the abdominal cavity. Excess abdominal fat is associated with an increased risk of obesity-related health problems such as type 2 diabetes, heart disease and certain cancers.

Incorporating waist measurement into the assessment of weight and health can provide a more accurate assessment of an individual's body composition and risk of obesity-related health problems. Some health organizations, such as the World Health Organization (WHO), recommend using waist circumference as an additional measure to BMI for assessing risk of obesity-related health problems.

There are several reasons why waist measurement can be a more reliable indicator of health than BMI alone:

1. Waist measurement takes into account differences in body shape: As mentioned earlier, BMI does not differentiate between fat and lean mass, meaning that two individuals with the same BMI could have very different amounts of body fat. Waist measurement, on the other hand, provides information about the distribution of body fat, specifically abdominal fat.
2. Waist measurement is more accurate for certain populations: BMI can be less accurate for certain populations, such as older adults, athletes and people with a higher muscle mass. This is because BMI does not take into account differences in muscle mass, which can lead to an overestimation of body fat in these populations. Waist measurement can provide a more accurate assessment of body fat in these groups.
3. Waist measurement is a strong predictor of health risks: As mentioned earlier, excess abdominal fat is associated with an increased risk of obesity-related health problems. Measuring waist circumference can provide valuable information about an individual's risk of developing these health problems.

It's clear that including waist measurement in the assessment of weight and health can provide a more accurate indicator of body composition and risk of obesity-related health problems, especially for certain high-risk groups.

Waist To Height Ratio

To calculate waist to height ratio (WHtR), divide your waist measurement by your height. For example, if your waist measures 35 inches and you're 6 feet tall (72 inches), your WHtR would be 0.49. This is within the healthy waist to height range of 0.4 to 0.49, which indicates no increased health risks. On the other hand, a ratio of 0.5 to 0.59 would indicate an increased risk of health issues, while 0.6 or more represents the highest risk.

To use waist measurement to modify the BMI calculation, you can use the following formula which includes your WHtR:
BMI = Weight (kg) / Height (m)² + Waist (cm) / Height (cm)

This modified BMI formula takes into account weight, height and waist circumference, which can provide a more reliable assessment of body fat and the associated health risks.

Other Factors

It's important to remember that BMI is only one factor to consider when assessing your overall health. Other factors such as diet, physical activity and genetics can also play a role in your overall health and well-being. A healthy lifestyle, including a balanced diet and regular exercise, is key to maintaining a healthy weight and reducing the risk of health problems. If you're concerned about your weight or BMI, it's always a good idea to speak with a healthcare professional for guidance and advice. They can help you assess your risk for health problems associated with excess body fat and develop a plan to achieve and maintain a healthy weight.

In conclusion, calculating BMI is a simple and convenient way to determine whether you're at a healthy weight for your height. While it's not a perfect measure of body fat, it can be a useful tool for healthcare professionals to assess the health risks associated with being underweight or overweight. By maintaining a healthy BMI, you can help to reduce your risk of developing a range of health conditions such as heart disease, diabetes and certain cancers.

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