Most health facilities and fitness centers use BMI as a measure of how fit one is. However, what really does your BMI say about your body fat? Is it the best tool you can use to measure your body fat?

In this article, we provide answers to these and other questions related to BMI. We also highlight some of the other body fat measurements you may want to consider.

The Definition of Body Mass Index

Body Mass Index aka BMI is a simple mathematical formula used to find if an individual’s weight is within the right weight range. It commonly used in hospitals and by fitness experts to instantly determine whether an individual has too much or too little weight for his or her height.

There are two ways you can tell your BMI. You could use an online calculator or you could do the math yourself.

Either way, you will need to have two measures, your height and your weight.

Using an online calculator is the easiest way to go about it. You will simply need to enter your height and weight to get your BMI.

You will then use the index to check whether you are of a healthy weight or if you are underweight, overweight or obese.

A body mass index of below 18.5 means you are underweight, while a BMI of 25.0 means you are either overweight or obese.

What is the purpose of BMI?

The purpose of BMI is to tell you or your physician or your fitness instructor how healthy you are.

If your BMI falls in the underweight range, there is a risk. It tells you that something is not right. Maybe you are not eating enough or you are suffering from a condition that needs immediate medical attention.

Similarly, if your BMI falls in the overweight or obese range, there is also a danger. Only that now the danger is of a different kind.

Being overweight means you are more likely to have high blood pressure, to get Type II diabetes, or to have a higher likelihood of getting a heart disease.

For those who are training, a BMI can help you to roughly tell whether you need to burn more fat. This is because if you are overweight or obese, then your body is most likely carrying more fat than it needs to.

Hence fitness experts may use it to recommend fat-burning exercises.

This means you really don’t have to worry about your body mass index. Simply consider it as a symptom that tells you whether or not you need to take any action.

Is it the best measurement for body fat?

Unfortunately, even though BMI is a very good indicator of the amount of body fat you are carrying, it is not a direct measurement of your body fat percentage.

“Why is this?”

This is because its formula takes into account only two simple measures of height and weight. The weight part is not only composed of your body fat. It also includes your muscles which also carry a significant weight. Unfortunately, the formula does not account for muscle weight.  

So for those who are really muscular or athletic, their BMI may reveal that they are overweight. This may wrongly imply that they have excess body fat. However, it is usually just the weight of the muscles interfering with the calculation.

Based on this fact, it is clear why BMI cannot be relied on as a good measurement of body fat.

If you are not athletic or muscular then it is probably a decent measure of the amount of body fat you are carrying. It is also really inexpensive compared to the other methods of measuring body fat.

However, if you are built and you’ve got good muscle on your frame, then you may want to consider other more accurate measurements of body fat.

The formula also does not account for differences in bone density. It is a fact that some people have heavier bones than others. Thus, they may have a high BMI that would wrongly imply they are not fit.

What are other body fat measurements are there?

There are numerous other ways to estimate the amount of fat you are carrying. Some such as multi-compartment models, 3D body scanners, bioimpedance spectroscopy and air displacement plethysmography are expensive and rarely used.

The more affordable ones include the use of body circumference measurement, the use of skin calipers measurements and the use of DXA (Dual-Energy X-ray Absorptiometry).

You probably don’t plan on buying an X-ray machine to measure your weight so let’s focus on the first two.

Body Circumference Measurement

The shape of the body is often one of the easiest ways to tell if you are overweight. Several militaries across the world including the United States Army, use the body circumference measurement to tell how fit a potential recruit is.

The method simply entails measuring the body circumference at different levels using a measuring tape.

The measurement is then used to calculate body fat percentage using a specific mathematical formula. This measurement is in no way affected by muscle weight or bone density making it a more accurate than BMI.

Use of Skin Calipers

Skin calipers have been used to measure the percentage of body fat for over five decades. The method simply requires the use of calipers to estimate the level of subcutaneous fat.

Specific sites on the body including the chest, the abdomen, and the tricep are calipered to get the thickness of subcutaneous fat.

This measurement is fed into free online calculators to complete the calculation.

The measurement error is often very low for this method when compared to BMI making it more accurate.

What to do if you have excess body fat?

You need to seriously exercise and to watch your diet. Serious exercise and cardio will help you to burn the excess fat. With regards to your diet, you may need to reduce your caloric intake or to eat less processed foods.

Bottom Line

BMI is a good estimate of the amount of body fat one is carrying. However, it is not the best. It has a few flaws including the fact that it doesn’t take muscle weight into account. Combine it with other inexpensive methods such as the use of skin calipers and the use of body measurements for a more accurate estimation of body fat percentage.