Buoyancy is the force on a body making that body to rise or move upwards.
ARCHIMEDES PRINCIPAL.
The upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces and acts in the upward direction at the center of mass of the displaced fluid.
Buoyant force = Pressure at bottom of the object - Pressure at the top of the object.
Pressure exerted by the fluid depends upon many characteristics such as density, volume, etc.
Pressure at the bottom of the object > Pressure at the top of the object immersed in a fluid.