How your BMI is calculated

[Firefly]

Origionally written by dawg, reposted by Sara;

Dawg was so nice as to take it upon himself to explain just exactly how the instant BMI calculators work. I think it's pretty interesting myself. There are a few links at the bottom as well if you want some more reading.

--------------- Calculating BMI ---------------
Weight pounds
----------------------------- x 703
height (inches) x height (inches)

Here's an excel forumula:
=((pounds(inches*inches))*703)

Here's my stats in the formulas:

270.5
---------- x 703 = 32.9
76 x 76

=((270.5/(76*76))*703)

Now something to bear in mind.

BMI is based on 'averages' for a 'normal' human being. Muscle mass skews the calculations. Here's an example.

I have a friend, he is 5 feet 4 inches tall. He weighs 240 pounds.
So that is:
((240/(64*64))*703 = 41.2
Therefor my friend is morbidly obese and qualifies for weight loss surgery.

Now here comes the catch.

My friend has a bodyfat of 6%. He is entirely lean muscle (and terrifying) but this clearly shows that the BMI calculation is flawed.

You should always get a body fat assessment to truly validate your BMI classification!

--------------- BMI Calculator Links ---------------

(Provided by the Department of Health and Human Services, Centers for Disease Control Prevention)
http://www.cdc.gov/nccdphp/dnpa/bmi/adult_BMI/english_bmi_calculator/bmi_calculator.htm

I also have used:
http://www.bmi-calculator.net/

--------------- BMI Chart ---------------

Super Obese: 50+ BMI
Morbid / Class III Obesity: 40 to 49.9 BMI
Class II Obesity: 35 to 39.9 BMI
Class I Obesity: 30 to 34.9 BMI
Overweight: 25 to 29.9 BMI
Average: 18.5 to 24.9 BMI
Underweight: Below 18.5

[dawg]

I think I'll rustle up a calculator in Excel for folks to download.

[The New Me]

I dont get it help me out here

I weigh

274 I am 5' 10" tall how do I figure it out

[Firefly]

According to http://www.bmi-calculator.net/ (http://www.bmi-calculator.net/)


You have a BMI of 39.31.

[dawg]

As an equation it's:

You need the square of your height (in inches):
5' 10" = 70 inches
70 x 70 = 4900

Divide your eight by 4900
274 / 4900 = 0.0559183673469388

To get your BMI:
0.0559183673469388 x 703 = 39.31061

Now, the reason you use the wierd 703 number is because the BMI calculation for the US is converted from the internation metric system.

[Firefly]

Showoff.

:bolt:

[The New Me]

Thank You very much

[dawg]

Oh and just incase you were curious and wanted to see the metric calculation.

Weight in Kilograms / height in meters squared

The New Hope's Metric stats:
Height: 70 inches = 1.778 meters (70 x 0.0254)
Weight: 274 lbs = 124.55 kg (274.5 / 2.2 )

Height Squared = 3.161284

BMI (Metric) = 124.55 / 3.161284 = 39.4

Yes, that does indeed mean that your BMI is different depending on what calculation you use. Why? The US system is a "ballpark" to keep it simpler.

That and 39.3 and 39.4 are pretty much the same thing.

And yes, I did fail math in school. So if it's all wrong - tough.

[PhotoNut]

--------------- BMI Chart ---------------

Super Obese: 50+ BMI <----------------------------------Where I started.
Morbid / Class III Obesity: 40 to 49.9 BMI
Class II Obesity: 35 to 39.9 BMI
Class I Obesity: 30 to 34.9 BMI <------------------------Where I am now.
Overweight: 25 to 29.9 BMI
Average: 18.5 to 24.9 BMI
Underweight: Below 18.5


I need to lose 24 pounds to be Overweight. I think I just found a new goal! :nod: