The gravitational potential energy of an object is always measured relative to the question 5 options: surface of earth. position of maximum mechanical energy. location where the object's kinetic energy is zero. reference level from which the height is measured.

the assumption is usually made that the zero of gravitational potential energy is the surface of the earth and that the potential energy is proportional to the height above the earth's surface. This is an approximation which is only valid near the surface of the earth, but is fine for baseballs and other common applications of gravitational potential energy. If you are in a room, it is logical to just call the floor the zero of gravitational potential energy, and measure the energy of an elevated object with respect to the floor.