What is the formula to check BMI?

In this article I will show you how to calculate..

What is the formula to check BMI

What is the formula to check BMI?

In this article I will show you how to calculate your BMI and how to find your weight category. BMI is a measurement which determines which weight category a person belongs to.

Depending on their height and weight, a person can belong to one of the following weight categories:

  • underweight (BMI less than 18.5)
  • normal weight (BMI between 18.5 & 24.9)
  • overweight (BMI between 25.0 & 29.9)
  • obese (BMI 30.0 and above)

 

If your math is a little rusty, that’s ok. Calculating BMI is straight forward, the formula is easy to compute and I will provide step by step examples.

In fact, the simplicity of this formula was part of the reason for its success (and also it’s main criticism).

It was developed by Belgium Statistician Adolphe Quetelet approximately 150 years ago.

This was before the era of electronic calculators; any formula used to indicate weight status needed to be easy for physicians to manually calculate.

Only the height and weight values of a person are needed in the equation.

How To Calculate BMI

Imperial (US) Method

Imperial Body Mass Index Formula

The imperial formula accepts height measurements in inches and weight in pounds. It’s popular in the US where the imperial system is mostly used.

Many people know their height in feet and inches, but not in inches only.

If this applies to you, we need to convert your height into inches so we can use it in the equation. There are 12 inches in a foot, so multiply your number of feet by 12 and add them to the number of extra inches.

For example, if your height is 5 feet 10 inches, multiply 5 by 12 (which gives 60″) and add them to the extra 10 inches (which gives 70″).

Now we have the right measurements we can use them in the formula.

There are three simple steps for computing BMI with imperial values:

  1. Multiply your weight in pounds by 703.
  2. Multiply your height in inches by itself
  3. Divide the figure from step 1 by the figure in step 3.

 

The resulting number is your BMI. Compare this BMI value with the weight status table below.

Example:

Jane weighs 150lbs and is 5 feet 4 inches tall. She wants to know if she is overweight.

Jane’s height in inches is (5 * 12) + 4 = 64″

1. Using the first part of the formula we multiply her weight by 703. 150 * 703 = 105450

2. Using the second part of the formula we multiply Jane’s height by itself. 64 x 64 = 4096

3. Finally we divide the first figure by the second. 105450 / 4096 = 25.74

Jane’s BMI is 25.74

We compare this value to the weight categories listed on the BMI table and find that she is overweight.

Metric Method

Metric Body Mass Index Formula

The metric formula accepts height measurements in meters and weight in kilograms. If you know your height in centimeters only, simply divide the number of centimeters by 100 convert it to meters.

For example, a person who is 183cms tall is 1.83m tall (183cm / 100 = 1.83m).

Using the metric formula is even easier than the imperial method as it’s a two step process

  1. Multiply your height by itself.
  2. Divide your weight in kilograms by the value calculated in step 1.

 

The resulting number is your BMI. Compare this BMI value with the weight status table below.

Example:

Paul weighs 150kgs and is 1.8m tall. He wants to know if he is overweight.

1. First we multiply Paul’s height by itself: 1.8 x 1.8 = 3.24 ²

Next we divide Paul’s weight by his height in meters ² just calculated: 150 / 3.24 = 46.3

Paul’s BMI is 46.3

We compare this value to the weight categories listed on the BMI table and find that he is obese.

BMI Weight Status Categories

The weight status categories opposite, are those currently used by the Centers for Disease Control and Prevention (CDC). They are suitable for adults who have stopped growing.

For children and teens who are still growing, the CDC base the weight categories on a BMI percentile. A child’s weight status is based on where their BMI value lies compared to children of a similar age.

BMI WEIGHT CATEGORIES
BMIWeight Status
Below 18.5Underweight
18.5 – 24.9Normal
25 – 29.9Overweight
30.0 +Obese

Daniel Messer, RNutr, CPT

We eat clean, are always motivated and helpout beginners in need. We sell guides on Cutting, Bulking and Muscle Building. Checkout our website!

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