The principle of displacement was first discovered by a Greek physicist named Archimedes. In basic terms, displacement happens when an object is immersed in liquid and the liquid is pushed out of the way for the object to take its place. This normally involves some of the liquid spilling out, or being displaced, of the container. The volume of the displaced liquid is measured and this shows the volume of the immersed object. This method is used to weigh ships and may also be used to check your weight without a scale.
Things You'll Need
Bathtub or tape
Fill the bathtub with enough water to cover your entire body when fully submerged. Mark the water level with a grease pencil or tape.
Submerge yourself in the tub and have someone mark the new water level.
Measure the length and width of the tub in centimeters. Measure the distance from the bottom of the tub to each of the two water level marks in centimeters. Multiply the length of the tub by the width of the tub by the height of the initial water level. This gives you the volume of the water in cubic centimeters. Repeat this multiplication with the height of the second water level.
Subtract the volume of the first water level from the volume of the second water level. This is the measurement of the water displaced when your mass was submerged in the tub.
Divide this number by 1.01 to calculate your weight in grams. Divide this number by 453.59 to convert this number to your approximate weight in pounds.
This method may be used on any object that may be safely submerged in water.
This method provides you with a close approximation of your actual weight, but a scale or other calibrated device must be used for real accuracy.