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Body composition calculations (How to)

Stack_it

Stack_it

Member
Dec 21, 2010
26
3
#1
With a quick little search you can find an online calculator for just about anything. Well if you like to do things yourself thenheres how to make some of the basic calculations.

Body mass index (BMI)
- Used to determine whether a person is at a healthy body weight.
- Muscularity can cause inaccuracy.

How to calculate:

Weight(kg) divided by height(m) squared

1kg = 2.2lbs and 1m = 39.25 inches

I'll use myself as an example. I'm 6' tall 183lbs this morning. So using the conversions above that makes me 1.83 meters and 83.1 kg's.

83.1 divided by 1.83 squared (square your height first) so that makes it 83.1 divided by 3.34. That means my BMI is 24.88

BMI Less than 20 — Under Weight

BMI 20-25 — Normal Weight

BMI 25-30 — Over Weight

BMI 30-40 — Obese

BMI Over 40 — Severely Obese


I fall into the normal range. One thing to keep in mind with bmi is that muscularity plays a big role. As you can see I'm close to being overweight at only 183lbs. That's because I have little fat and decent muscle. So if it say you are overweight it does not mean that you are unhealthy. This is just to make a quick assessment of whether you are at a healthy weight. If you feel you are at a healthy weight and your bmi says otherwise then you should have your body fat percentage measured to be sure.
 
Stack_it

Stack_it

Member
Dec 21, 2010
26
3
#2
Calculating optimal body composition.

Research suggests that a range of 8-22% body fat is optimal for men and 20-35% for women. Obviously most of the men reading this will want to be below 15%. The 22% is a little high IMO but that's mainly for your everyday guy on the street.

In order to do this calculation you need to know your current bf% or atleast a very close estimate. I recommend you have it tested with metal calipers. The electric handheld testers are very inaccurate and the other methods are expensive and hard for the every day lifter to do. Once you know your body fat percentage here's how to calculate your optimal weight in order to get to your optimal bf%

I have right at about 10% bodyfat so I won't use myself for this example. Instead I'll use someone with a higher bf%.

Test subject: 5'11" 212lbs and 16% bodyfat

First calculate what your fat free weight is. Fat free weight Is the amount of total body weight contained in bones, organs, and muscles.

Total body weight - fat weight = fat free weight
In this case we have 100% - 16% = 84%

This means that 84% of total body weight I'd fat free weight. Which means the fat free weight of this person is 178.08lbs (212 x 84%)

Let's say that this person wants to reach 10% bf. The formula to figure out what weight he needs to reach is "fat free weight divided by (1 - optimal % fat) make sure you express the optimal percent as a decimal.

Here's what it would look like.
178.08 divided by (1 - .10) so 178.08 divided by .9
That equals 197.86lbs

So assuming that this person maintains there current muscle mass he would have to drop down to 197.86lbs to reach his 10% bodyfat goal.

When doing this calculation it is best to set goals in increments of 5% and then recalculate once you hit each goal in order to compensate for any muscle mass gained or lost. On average with out the help of aas or thermogenics it should take about 6 weeks to drop 5%. assuming diet and training are correct.

If anyone is confused or unclear about a certain part then let me know and I'll try to explain. Also I apologize for any typos as this was all written from my phone.
 
Dangling Unit

Dangling Unit

VIP Member
Jan 2, 2011
672
75
#3
BMI is a disgusting way of figuring out one's health and should never be used, let alone mentioned. For example, my BMI is 32 - obese, yet I'm sitting around 5% body fat. Hardly obese.

Another important aspect you forgot to include, is weight loss won't be linear for fat loss. Some muscle weight is expected to be lost (without drugs),so if the same guy were to drop weight to 197.86#, it's almost gauranteed to not be 10%. It'll probably be more of 11 or 12%.

Oh, and 1-m = 39.37-in (to four significant figures).
 
Last edited:
Stack_it

Stack_it

Member
Dec 21, 2010
26
3
#4
BMI is a disgusting way of figuring out one's health and should never be used, let alone mentioned. For example, my BMI is 32 - obese, yet I'm sitting around 5% body fat. Hardly obese.

Another important aspect you forgot to include, is weight loss won't be linear for fat loss. Some muscle weight is expected to be lost (without drugs),so if the same guy were to drop weight to 197.86#, it's almost gauranteed to not be 10%. It'll probably be more of 11 or 12%.

Oh, and 1-m = 39.37-in (to four significant figures).
I agree bmi can be off but if you notice I did say that muscularity could effect accuracy. It is a good tool for someone who has never lifted or excercised on a regular basis to give themselves an idea of whether or not there weight is in a healthful state. It has no place in the bodybuilding world. That being said many people come to these forums who are brand new to excercise and nutrition looking for help and the bmi calc was added for them.

I dont think you read my post very thoroughly or else you would have noticed that I said "assuming the test subject maintains his current muscle mass" the weight he would need to reach for his goal bf% would be 197.xx

It's a tool used to help not an exact science. If you read the post you would have also noticed that I recommended anyone using that formula to calculate it to lose about 5% at a time so that after they hit there goal weight to reach that 5% loss they could re calculate to make up for lost or gained muscle mass.
 
tommyguns2

tommyguns2

Senior Moderators
Staff Member
Dec 25, 2010
4,586
1,843
#5
I was extremely unhappy when my insurance company required use of BMI to calculate my risk level. It caused me to pay a much higher premium, when in fact I'm much more healthy than many with significantly lower BMIs. I suppose an actuary doesn't care about any particular data point, they've got a data set that I'm in and that data set has a higher chance of croaking this year....
 
Stack_it

Stack_it

Member
Dec 21, 2010
26
3
#6
I was extremely unhappy when my insurance company required use of BMI to calculate my risk level. It caused me to pay a much higher premium, when in fact I'm much more healthy than many with significantly lower BMIs. I suppose an actuary doesn't care about any particular data point, they've got a data set that I'm in and that data set has a higher chance of croaking this year....
Insurance companies using bmi is just a way for them to make more money.
 
AWARE72

AWARE72

MuscleHead
Oct 17, 2010
323
18
#7
I was extremely unhappy when my insurance company required use of BMI to calculate my risk level. It caused me to pay a much higher premium, when in fact I'm much more healthy than many with significantly lower BMIs. I suppose an actuary doesn't care about any particular data point, they've got a data set that I'm in and that data set has a higher chance of croaking this year....
YA ding ding ding...I lloking at my agent and asking do I look like I obese? but yes that use BMI to underwrite policies
 
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