[Swordmaker]

But the only easy and cheap way to measure body volume is by total immersion. It makes no difference how massive or dense a body is. Once it is totally immersed you have its volume. But weight is a separate and independent measurement.

If a body or object floats in the liquid, it also is a quick and easy method of determining mass. It will only work for mass if the object floats, meaning that the object is less dense than water. Every human body that I am familiar with is less dense than water. Ergo the water displaced by the floating body exactly equals its mass/weight. Force total immersion then the water displaced by the immersed body exactly equals it's volume.

[Swordmaker]

Please ignore my first paragraph in the last post. JS1138 is right on the freefall determination of mass. The method I described still requires a known acceleration to work. Sorry about that. Second paragraph is still accurate.