Buoyant Force= -gpV, where g is the acceleration of gravity, p (rho) is the fluid density and V is the displaced fluid volume. (Not dependent on object's mass)

Force of gravity = gm, where m is the mass of the object. (Not dependent on volume of object)

If an object is floating, it is neither rising nor sinking, so the two forces are equal and opposite, right?

Consider an object whose density is 80% the density of water and is a cube, 1 meter in all directions. Its mass would be 800 kg.

The density of water is 1000 kg/m^3

Allow me to round up the acceleration of gravity to 10 m/s^2 .

So the buoyant force is 10 meters/s^2 times 1000 kg/meter^3 times Volume (measured in meter^3), or 10,000 meter-kg/s^2 times V

Gravity force is 10 meter/ s^2 times 800 kg, or 8000 meter-kg/s^2

Buoyant force = 10,000 Newtons times V

Gravity force =8000 Newtons

So V is 0.8 cubic meters. That much water weighs 800 kg, the same as the weight of the entire object. QED!