BMI Calculator

Calculate your body mass index (BMI) with the calculator below. Enter your height and weight to evaluate your BMI and compare with healthy individuals.

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• Body Fat Calculator
• Ideal Weight Calculator

How to Calculate BMI

BMI is calculated through a simple formula that was designed to put the ratio of weight to height in a nice round number that could be studied over populations.

The following is the formula for BMI

BMI = 703*Weight (lbs) / [height (in)]^2

In SI units the formula is the following:

BMI= Weight (kg)/ [height (m]^2

Both of these formulas will give you the same value for BMI.

As is covered more in depth in the following paragraphs, BMI is not an accurate representation of health on and individual level. It should only be used on population scales because it does not take into account things like muscle mass and body fat.

Body Mass Index

The term “body mass index”, also know as the acronym BMI, refers to the ratio of human body weight to squared height. Originally developed in 1830-1850 but officially used in a paper in 1972, is a way to easily track unhealthy weights in large populations.

The following list is the guideline for ranges of healthy BMI

0 – 15: Very severely underweight
15 – 16: Severely underweight
16 – 18.5: Underweight
18.5 – 25: Normal Range (healthy)
25 – 30: Overweight
30 – 35: Obese class I – Moderately obese
35 – 40: Obese class II – Severely obese
40: Obese class III: Very severely obese

BMI is quick and easy to calculate, which is why it has gained rapid popularity over the last couple decades. That doesn’t mean it’s always an accurate way to measure health. For example, athletes and individuals with more muscle will have results that may indicate they are overweight, when in reality they are completely healthy. A more accurate representation of your health would involve a measure of body fat % and lean muscle %. 

If you do happen to fall on the high end of BMI, and you are not an athlete, you may need to look at losing some weight. You can start by calculating your daily calorie intake, and eating less than that. For a good place to start, click here.

 Is BMI Good or Bad? 

Let’s dig a little deeper into BMI and it’s purpose vs. what it actually achieves. The goal of the BMI is to estimate the health of an individual based on the amount of tissue mass they hold. In itself this doesn’t actually mean much of anything, it’s just another number. To make this number meaningful, the WHO (world health organization) and other health institutes set out to study populations, and came up with the classes you see above. These are the official classes set out by the WHO, but there are even some disputes on what the cutoff points of healthy and overweight/underweight should be. In addition, people of different ethnicity can have varying cutoff points. This is a result of genetic differences in large populations with regard to how much fat they hold, and how that fat effects their health. For instance, people of European decent are genetically at greater risk for cardiovascular disease at the same BMI as other populations. With that said, because this entire metric was developed to study people on a global scale, it is actually very accurate when it comes to studying the health of large populations. On and individual level, it can be almost useless. 

For example, as mentioned previously above, muscle mass weighs much more than fat. Someone that is very muscular will almost certainly fall in the overweight or obese ranges, but really they are extremely healthy. Additionally, because this is a ratio of body weight to squared height, if all body dimensions increase, and the mass scales naturally with height, then the BMI of taller people will be uncharacteristically high. For this reason, and many others, you should not take BMI as an indicator of health for yourself. When talking about weight and health, body fat % is a significantly better metric to use. ​

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