Your weight is determined by two things: your mass (the amount of matter/energy in you, plus a tiny adjustment for such things as information content etc, that we don't normally allow for because they are negligible except for certain theoretical purposes) times the intensity of the local gravitional field. So for example, if you have a mass of 50kg and the local gravitational field happens to be 9.8 Newtons per kg, then your weight will be 490 Newtons, about the same as 490 medium-sized apples or one hundredth of a sizeable African Elephant; a centi-elephant so to speak.  In turn, the local gravitational field is determined by the mass, shape, and distance of nearby bodies. For example, our planet happens to be roughly spherical and has a mass of about 6E24 kg (about 12E22  centi-elephants) and a radius of about 6000 km, which works out at about... 9.8 Newtons per kg. You need to be careful about the implications though. Your weight is a relative thing. Suppose you are in space, but you carry a scale about with you so that you can tell when you are in a gravitational field. Every now and then you weigh yourself, and you say: "Good! A weight of practically zero! Nothing to worry about."  Meanwhile, you and your scale might be falling faster and faster towards Earth, and when you hit it (or its atmosphere, even) there might be some bad news for you!