Volume = length × width × height
The displacement can is filled with water above a narrow spout and allowed to drain until the water is level with the spout.
As the irregular object is lowered into the displacement can, the water level rises. Since the level was already up to the bottom of the spout, all the displaced water comes out of the spout and is collected in a measuring cylinder.
Thedisplaced water in the cylinder occupies the same amount of space that the object now does in the can, which means that their volumes are the same.
If the object fits directly into the measuring cylinder, fill the cylinder to a suitable level and take the reading. Carefully lower the object into the cylinder. The water level rises. Take the new reading.
The difference between readings is the volume of the object.