Archimedes' principle

If we want to determine the volume of an egg, we need one egg and a measuring cup. In the picture above, the measuring cup is filled with exactly 300 ml of water.

If we put the egg in the measuring cup it sinks and displaces exactly the same volume of water like its own volume is. The markings show that the water now reaches up to the 360 ml marking.

The water level rose from the 300 ml marking up to 360 ml. The difference is 60 ml. Therefore, the egg has a volume of 60 ml.