Quote Originally Posted by killersheep
Does anyone know the equation to calculate this?
The most accurate method is to weigh yourself underwater. Then do some maths :

Body density = Wa/(((Wa-Ww)/Dw)-(RV + 100cc)), where Wa=body weight in air (kg), Ww=body weight in water (kg), Dw=density of water, RV=residual lung volume, and 100cc is the correction for air trapped in the gastrointestinal tract.

The problem is you need a f*&^&** big tank and a degree in physics to work it out.