What Is Body Mass Index: What You Need to Know

What Is Body Mass Index: What You Need to Know

Body Mass Index (BMI) is a way to measure body fat. It is used as a tool by individuals, fitness professionals and health-care providers to determine whether you are underweight, normal weight, overweight, or obese. It is based on your weight and height. ​​You’ve probably calculated your BMI before, most likely using one of the many online BMI calculators.

You might have judged yourself harshly based on your BMI. I have had clients tell me that they have consciously tried to ensure they are closer to ‘underweight’ than ‘overweight’ on the scale or who were very upset and put off when they read their BMI. I remember calculating my BMI for the first time when I was about 14 years old and being very distressed about where I was too. I wasn’t aware of the limitations of the BMI this post is here to breakdown the reality of it.

Why Body Mass Index is important to understand

The Body Mass Index is important because it is an efficient general indicator of overall health that can be used to predict the risk of some diseases such as diabetes and heart disease. These measurements are a way to measure the “weight” of the population. However, it does come with some major flaws which we’ll go into a little later. We don’t yet have an equally accessible and efficient tool to take such measurements, so, although it is flawed, for now it is here to stay. We can ease the limitations of the BMI by not seeing it as the be or end all and also by supplementing it with other body composition tools, if measuring your body composition is an important and healthy thing for you to do. This post will also go into alternative tools.

You can be healthy and have a high-risk BMI score

The BMI is intended to indicate your health but because BMI calculations are based purely on height and weight they are not a reliable way to measure health or fitness. Factors such as muscle mass, blood pressure, body fat percentage and lifestyle are all important health considerations that are not taken into account. For example, someone who has a lot of muscle mass relative to their height can easily be identified as “overweight” using the BMI formula. This demonstrates that you can be healthy and have a high-risk BMI score at the same time.

The Problematic History of BMI

Another major flaw with BMI is that it is based solely on a study done of European men. Early 19th century Belgian mathematician and statistician Adolphe Quetelet invented the BMI index based on a study he did which only elected European men. So, it highly problematic that it was later adopted by the World Health Organization (WHO) and is now commonly used as a measure of obesity and overall health of people of all ages and races. This alone might make you want to disregard the BMI altogether, and understandably so. Alternatives are offered to you below if you do want a way to measure your body fat.

Body Mass Index Calculator


BMI Calculator
Use this calculator to check your body mass index (BMI).
Please enter value between 125 and 225.
Please enter value between 10.0 and 500.0 ( one decimal ).
Calculate BMI
Use this calculator to check your body mass index (BMI), which can be a helpful tool in determining your weight category. Or, use it to calculate your child’s BMI.

Here are some other ways you can measure your health and fitness

Now that we’ve established that BMI, although BMI is a widely used, does have some major limitations, let us go over some alternative methods you can use alongside of instead of BMI.

A more accurate way to measure disease risk is to measure subcutaneous fat – fat under the skin – around the abdomen. This is an indicator of visceral fat around your organs which is associated with diseases including diabetes, heart disease and stroke. Of the alternative tools listed below, numbers 3 to 5 specifically indicate subcutaneous fat around the abdomen, indicating that high-risk visceral fat, and so are particularly helpful in assessing health risk.

Make sure taking these kinds of measurements of your body feels empowering. Your health and fitness journey gets to be empowering. It is not about self-scrutiny. Remember to make choices from a place of love and compassion!

Bioelectrical impedance analysis (BIA)

This method uses a small electrical current to estimate body fat in ratio to total body wight by measuring the resistance to a tiny electrical current in the body. BIA is available in many fitness centres and gyms.

Dual-energy X-ray absorptiometry (DXA)

Another way to measure body fat in ratio to total body weight. This test is not easily available and has to be done through a health-care provider. It is also flawed because DEXA machines are unable to measure the bones in people who weigh 300 pounds or more or who are taller than 6 feet . This method is often considered more accurate than BIA but studies show the results of the two tests to be surprisingly similar.

Waist Circumference

This is a simple measurement of the distance around your waist and is used as an indicator of subcutaneous fat around the abdomen.

Waist-to-hip ratio (WHR)

The ratio of the circumference of your waist to the circumference of your hips. This is used as yet another measurement of overall body fat distribution. Because this is another measurement of subcutaneous fat around the waist it is also an indicator of risk of certain diseases as mentioned above.

Skinfold Thickness

Another measurement of subcutaneous fat except not just around your waist and stomach, skinfold thickness can be measured anywhere in the body. It is a measurement taken by pinching the skin at various points of the body. Typical areas to be masured include the biceps skinfold – the front side of your upper arm, the triceps skinfold – back side of your upperarm, your subscapular skinfold – under your shoulder blade and your suprailiac skinfold – just above your hip bone.

Note that all these methods also have limitations. There is no one tool to measure health and fitness; a combination is required. It’s recommended to consult with a healthcare provider or a nutritionist to determine which method is best for you and also how to interpret the results. Health professionals not only help ensure you have the correct information but they can also help to provide a safe container in which for you to address an often very vulnerable, tender part of our lives – our weight and our health

Key takeaways

    • BMI is not a reliable indicator of health or fitness 
    • BMI was created based on a study done only on European men 
    • There are many other ways to measure body fat if that is something you want to do 
    • Subcutaneous fat around the abdomen indicates visceral fat – fat around your organs. That is the fat that is associated with high risk for certain diseases.
    • You are deserving of love and kindness towards yourself and from all others regardless of your BMI, weight or subcutaneous fat!

More Resources

Eating Healthy: Some Simple Tips – ideal if you are looking to lose body fat

Maintaining a Healthy Diet while Pregnant – ideal if you are pregnant

What Exercise burns the Most Fat – ideal if you are looking of exercises that burn body fat


Written By Bea: Female fitness expert at MotivatePT – Reps Level 3 Qualified / Pre & Post Natal


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