To determine an object's buoyant force use

It doesn’t matter whether the object floats or sinks. The formula to calculate buoyant force is same. Just weigh the fluid which the object displaces. This weight represents the magnitude of the buoyant force acting on the object.

As we know that, weight of the displaced fluid

= (volume of the displaced fluid)*(density of the fluid)*(acceleration due to gravity).

However, a body sinks if its weight exceeds the buoyant force acting on the body due to its entire volume.