What is the Body Mass Index?

Amy Hunter

Body Mass Index, or BMI, is the method medical professionals use to determine if someone is a healthy weight. Body Mass Index takes into account a person's height and weight to determine levels of body fat. BMI is typically used in individuals over 20, children and adolescents require a different formula to determine if they are a healthy weight.

Individuals who have a high BMI are at an increased risk for developing sleep apnea.
Individuals who have a high BMI are at an increased risk for developing sleep apnea.

Body Mass Index is an indicator of some types of disease. High BMI is often associated with cardiovascular disease, high blood pressure, type 2 diabetes, some forms of cancer, and sleep apnea. While BMI is an accurate indicator of your risk of obesity-related disease, genetics and lifestyle also have an effect on these conditions. Healthcare professionals use blood pressure, blood sugar, and cholesterol levels as well as family history when determining if someone is at risk for a particular disease.

A person with a BMI of more than 30.1 is considered obese and unhealthy.
A person with a BMI of more than 30.1 is considered obese and unhealthy.

Body mass is determined using the mathematical calculation weight in pounds multiplied by 703, divided by height in inches, squared. For people comfortable working with metric measurements, the calculation is more straightforward, weight (Kg), divided by height (M.), squared. There are many online BMI calculators available as well.

Body Mass Index calculations provide an objective assessment of weight. People with a BMI lower than 18.5 are underweight, those whose BMI is between 18.5 and 24.9 are in the healthy range, people with a BMI of 25 to 29.9 are overweight, and those with a BMI of 30 or higher are obese.

While people on either end of the BMI scale, who are either underweight or overweight, have the highest risk of developing health related complications, people who are within the healthy weight guidelines, who do not exercise, eat poorly, or smoke cigarettes are also at an increased risk of developing health related conditions. Similarly, there are things that someone with a high BMI can do to improve their health and reduce their risk of developing disease. Regular checkups to monitor blood pressure, cholesterol and blood sugar levels are beneficial. Physical activity, whether through a structured exercise program, or through lifestyle modifications such as walking, also improve health, even if weight remains the same.

A healthy body mass index is essential for good health.
A healthy body mass index is essential for good health.

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Discussion Comments


I'm not good at math so I don't use the mathematical formula to find out my BMI. There are charts and tables available that have scales for height at one axis and weight on the other. When you locate your height and weight, you can find your BMI and know whether you are normal weight or not.

I got my chart from my doctor, you can ask your doctor for one as well. It's also possible to get them online, but make sure it is the right one for you in terms of age group and gender, otherwise it might not be accurate.

I would also suggest people to visit their doctor if they want a more detailed analysis and help with losing weight. Some people take BMI results very seriously and create their own diets to lose pounds and get in the right BMI range. I don't approve of that. I think BMI is good for confirming what we already acknowledge about our health. It can help us become more conscious and make wiser decisions. But don't condemn yourself because of your BMI results.


As far as I understand, body mass index is not an exact or detailed description of your health or fitness level. It's a more general method of knowing what the body fat levels are like and what the risks for illness are.

So if someone's body mass index shows that they are obese, we can assume that they have high fat levels and are at high risk for various diseases. It's not exact, but it usually correct results and is a fast, easy and cheap way to assess someone's health. Since the number of heart patients and diabetics are increasing pretty rapidly in the U.S., I think the use of body mass index is important.

Very rarely, the body mass index might not be very applicable. Especially with athletic people, or very thin people. Because, BMI correlates with body weight and gives us insight on fat levels. So even though an athletic person might have a high body weight, they might not have much fat in their body, but their BMI would still be high. Similarly, if someone is very thin, the body mass index might assume that they have very little fat, when the opposite could be true.

Still, body mass index works for more than 90% of people and is a reliable way of measuring health.


I have one of those advanced scales that measure BMI and also fat percentage, total body weight and muscle and bone density. I input my height and age, it measures my weight and gives me all these numbers.

According to my age and weight, the scale says that I'm overweight but my BMI is 24.6. I know that's pretty close to overweight range, but it's still considered healthy.

So is BMI a better way of determining health than simply considering age and weight? Which number should I take more seriously, the age and weight analysis or the BMI?

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