What is the formula you use to determine the gravitational potential energy of an object?

Answer 1

Weight x Height = Potential energy

The units and the calculation are the same as for work. Work is force through a distance. Get the weight in the SI by multiplying the mass in kilograms by the acceleration due to gravity on earth like so:
1.00 Kg x 9.81 m/s2 = 9.81 Newton

The gravitational potential energy of a 1.00 Kg mass lifted 1.00 meter on earth will be:

1.00 Kg x 9.81 m/s2 x 1.00 m = 9.81 J

In the SI, you will give the answer in Newton meters or Joules

Answer 2

PE = mgh, that is, mass x gravitation x height. Or simply weight times height, since weight is already equal to mass times gravitation.

On Earth, you would usually use 9.8 (meters per second square) for gravitation.

If mass is in kg., gravitation in meters per second square, and height in meters, then the result will be in Joule.