what's wrong with my formula?

Question

I'm making a function which returns the body fat composition from below algorithm:

495/(1.0324-0.19077(LOG(waist-neck))+0.15456(LOG(height)))-450 // for men

495/(1.29579-0.35004(LOG(waist+hip-neck))+0.22100(LOG(height)))-450 // for women

I convert it into java language as below:

495/((1.0324f-(0.19077f*(Math.log(_waist-_neck)))+0.15456f*(Math.log(_height))))-450 // for men

and the values are:

_height = 70.86f; // 180cm & 70in
_waist = 35.43f; // 90cm & 35in
_neck = 19.68f; // 50cm & 19in
// values are converted from centimeter

in my way, it returns -25.125 But in http://www.calculator.net/body-fat-calculator.html site, which already is using this algorithm (see below the converter), I put theses values it returns 10.3

what is my wrong? is there any thing lost in my nested formula??

Answer 1

The formula expects the input in centimeters, not inches, and uses base-10 logarithm:

@Test
public void formula() throws Exception
{
    float _height = 180;
    float _waist = 90;
    float _neck = 50;
    double fat = 495/(1.0324f-(0.19077f*(Math.log10(_waist-_neck)))+0.15456f*(Math.log10(_height)))-450;
    System.out.println(fat);
}

Output

10.31526981020346