What Is BMI? How Is It Measured?

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Filling out a medical form and wondering what is BMI? Well, this happens to a lot of people when they first encounter the strange medical term.

BMI or body mass index is a measure of your weight in relation to your height. It is a tool widely used in healthcare settings to assess risk factors for certain diseases related to obesity.

But it is not a valid or even a diagnostic tool, nor do the healthcare workers rely only on it as much. Still, it is used in the medical community because it’s a simple, easy, and inexpensive method to check the general health of a person.

Let’s dive in to find more about BMI and how you can measure it.

What is BMI?

BMI is a measurement or calculation of your body’s size according to your height and weight. It is actually the person’s weight in kilograms divided by the square of height in meters.

In simple terms, it is the ratio of weight to height. The value is actually used to assess if the person is underweight, healthy, overweight, or obese. BMI is used to screen excess weight among the general population. It is an indirect measure of calculating the percentage of fat in your body.

Significance of Calculating BMI:

Although BMI isn’t as good a tool to give you accurate results, it is still used worldwide. Because it helps with body categorizations, it is considered highly significant in health care.

Professions of a certain kind, like the military, demand a normal BMI range because they need fit individuals. Nurses work in various other professions, apart from healthcare, and offer assessment checks. These are usually registered nurses that are credentialed in best LPN to RN programs, which makes them qualified to make all the necessary body assessments.

Similarly, BMI can be used as a tool by doctors to assess the overall health condition of a patient. The person in the overweight category is at high risk of developing a number of diseases, such as diabetes, hypertension, and certain other heart problems.

And a person in the underweight category is also prone to certain health conditions, which are less serious than the ones mentioned for overweight people. Healthy individuals can also use BMI to accurately assess their fitness level.

How is BMI Calculated?

Every single person, whether a healthcare provider or not, can calculate BMI at home by using simple formulas. As already mentioned, BMI is the ratio of a person’s weight to the square of height, there are actually two formulas that can calculate BMI depending on the units you are using.

  • Metric Formula:

The ratio of weight in kilograms to the square of height in meters.

BMI = weight (kg) ÷ (height) ^2 in meters

For example, a person with a weight of 45kg and a height of 1.4224 meters will have a BMI value of 22.2.

  • Imperial Formula:

Weight in pounds multiplied by 703 divided by the square of height in inches.

BMI = weight (lbs x 703) ÷ (height) ^2 in inches

For example, a person with a weight of 150 pounds and a height of 66 inches will have a BMI value of 24.2.

In children, growth charts and percentiles are used to measure BMI. Gender and age are also taken into account while calculating BMI in children.

There are different BMI cutoff points for children of different ages. A BMI above the 85th percentile is considered overweight, a BMI below the 5th percentile is considered underweight, and a BMI between the 5th and 85th percentiles is considered healthy.

Normal BMI Range:

A BMI of 18.5-24.9 is considered a normal healthy weight. BMI value of 25.0-29.9 is considered overweight while 30 & above is considered obese. If your BMI is below 18.5, you are underweight.

Risks of High BMI:

If your BMI is above the normal range, you are most likely at risk of developing certain diseases, such as

  • Coronary heart diseases
  • Type 2 diabetes
  • Hypertension
  • Sleep apnea
  • Several respiratory diseases
  • Stroke

Risks of Low BMI:

Having a BMI below normal also comes with certain health problems, such as

  • Weakness or fatigue
  • Malnutrition
  • Anemia
  • Weak immune system

Limitations of BMI:

When BMI was first used, the standard were the measurements of a healthy European male. Different races, genders, and age groups have different levels of fat or muscle in their body.

Also, BMI doesn’t discriminate between muscle mass and fat. As a man generally has more muscle mass than a female of the same age, males typically have a higher BMI, which doesn’t necessarily mean they’re unhealthy.

Similarly, athletes have a high BMI because of high muscle mass. So, BMI isn’t an accurate tool that can indicate high or low fat in the body.

Further, there are chances that a person with a high BMI may still have low body fat.

Alternatives to BMI:

If you’re concerned that a BMI value may not offer the best measurements for your health, there are a few alternatives you can consider. The following alternatives may be more accurate in assessing someone’s body fat:

  • Body Fat Percentage:

Body fat percentage is a measure of someone’s body fat that takes into account factors, such as muscle mass and bone density.

  • Waist-to-Hip Ratio:

The waist-to-hip ratio is another option that can give you a better idea of where your body fat is distributed. The ratio is more accurate than BMI in predicting obesity-related health risks.

  • Fitness Tests:

And finally, fitness tests such as the VO2 max test can give you a more complete picture of your overall health. Fitness tests are a great way to gauge your level of fitness and see where you need improvement.


BMI does not measure body fat directly, but it is a reliable indicator of the body’s weight to height proportions. BMI is not a perfect measure and has some limitations: It does not take into account gender, race, and age. But on the whole, it can provide a credible assessment of someone’s fitness.