Measure 2 cups plaster of paris and pour it into the bucket. Add 1-1/2 cups water to the bucket.
Stir the plaster mixture until it is free of air bubbles and has a thick, soupy texture. If necessary, add more plaster or water to get the desired texture.
Pour the plaster into a paper plate or other flat, shallow container, such as a tray, which will serve as a mold box. Make sure that the plaster is poured about an inch thick.
Let the plaster sit in the box for two minutes, so that the mixture is slightly more solid.
Put the mold box on the floor and step into it with the foot you wish to mold. Do not press down all the way to the floor, or your footprint will not have a bottom.
Hold your foot in the plaster for two minutes, until the mixture hardens further. Remove your foot from the plaster with care.
Leave the plaster to set overnight, or for at least 12 hours. Remove the plaster footprint from the mold box.