Body fat percentage calculation error

Hi Jillian,

Thanks for your response and thanks for using iHeartRate and caring enough about it to let us know of this issue.

In fact, while it may seem counter-intuitive, an INCREASE in neck size actually indicates a DECREASE in body fat percentage. Why is this?

Well, I don't quite know, to tell you the truth, but our formula is based on the US Navy's body fat percentage method. This method is meant to be an approximation accurate to within 2-3%.

Here are the exact formulas we use:

The formula for men (measurements in cm):

%Fat = 495/(1.0324-.19077(log(ABDOMEN-NECK))+.15456(log(HEIGHT)))-450

The formula for women (measurements in cm):

%Fat=495/(1.29579-.35004(log(ABDOMEN+HIP-NECK))+.22100(log(HEIGHT)))-450

As you can see from the formula, NECK size is subtracted from ABDOMEN and HIP size, which indicates it has an inverse affect on your body fat %.

The logic behind this is that the formula attempts to compensate for muscle growth which should, in fact, increase the size of your neck. We understand that this is not going to be an exact measurement (you will need other devices to determine that), but this formula as been proven to be an excellent approximation.

Here are some various links to external sources relating to this formula:

Body Fat % Calculators (Navy Method):

http://www.bblex.de/en/calc/navy.php
http://fitness.bizcalcs.com/Calculato...
http://lowcarbdiets.about.com/library...
http://www.healthstatus.com/calculate...

I hope this clears up any confusion and I hope that you continue to use and enjoy iHeartRate and if you have any further concerns and questions, we'd love to continue to hear your feedback.

Thanks,
Garry Seto
Co-Founder, Endloop Systems Inc.