Archimedes' principle states that the volume of the displaced water is equal to the volume of an immersed object. It also follows from this principle that the weight of the immersed object reduces; this phenomenon is known as buoyancy. This reduction in weight is equal to the mass of the displaced water. To calculate the weight of the displaced water, you need to know the water density, which varies with temperature.

Retrieve the density of water from the table given in the Resources. For example, if the temperature is 25 degrees Celsius, then the density of water is 997.13kg/cubic meter.

Divide the density in kilograms per cubic meter by 1,000 to convert it to grams per millilitre (cubic centimetre). In this example, the density is 997.13 / 1,000 = 0.99713g/ml.

Multiply the volume of the displaced water by the density to calculate the weight. For example, if the displaced volume is 450ml, then the weight of the water is 450 x 0.99713 = 448.7085 grams.