Thursday, February 25, 2010

Calculations

For those that wonder how I calculate the numbers (BMI, BF%, WHR) in my posts:

BMI = 703 * Weight / Height^2

BF% = 486.37 / (1 - 0.18745 * LOG(Waist - Neck) + 0.15187 * LOG(Height)) - 450

The BF% formula was developed by the US Navy.  While it isn't as accurate as calipers or body scans across all body types, I have found it matches up to the numbers I got when using calipers.  So I now pretty much use the formula!

Since I am 69" tall, this simplifies to:

BF% = 450 * (LOG(W - N) - 1.0585) / (6.8248 - LOG(W - N))

and a pretty good linear approximation to this (pretty much dead on at higher body fat %, but only differs by about 2% BF% at low body fat) is:

BF% = 11/8 * (W - N - 5)

For example, if you have a 16" neck and 34" waist, the real formula gives 15.9% compared to 17.9% using the linear approximation.  My current numbers, however, give 41.9419% (real) and 41.9375% (linear).  Regardless, I will be using the Navy formula for my postings.

Finally, the easiest one:

WHR = Wasit / Hip

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