How do you calculate the displacement of water?
1 Answer
There are two ways that this could be answered: (1) what volume does water occupy, and (2) how can the displacement of water be used to determine the volume of an object. These two things are related to one another.

The volume of water, in its liquid state, can be measured using fluid units (mL, L, kL) or cubic units (
#cm^3# ,#dm^3# ,#m^3# ). One milliliter (1 mL) of water occupies a volume of 1 cubic centimeter (#1 cm^3# ). One liter (1 L) of water occupies a volume of one cubic decimeter (#1 dm^3# ). One kiloliter (1 kL) of water occupies a volume of one cubic meter (#1 m^3# ). 
Because of the above relationship, water can be used to determine the volume of an irregular solid object. This is the principle that Archimedes used to solve the problem with the king's crown: a submerged object displaces a volume of liquid equal to the volume of the object.
Example:
To measure the volume of a set of keys, take a 250 mL graduated cylinder, filled to the 100 mL mark with water. Drop the keys into the water, and measure the total volume within the cylinder (the new volume to which the water has filled the cylinder). The volume of the keys is equal to the difference.