Archimedean Principle

To determine the volume of an egg you need an egg and a measuring cup. The measuring cup is filled with exactly 300 ml of water (picture on the left). If you put the egg into the measuring cup, it will sink and displace exactly the same volume of water as its own volume (picture on the right).

Because of the check mark on the measuring cup you can see that the water now reaches the mark of 360 ml.

Thus the water level has risen from the mark of 300 ml to the mark of 360 ml. The difference is 60 ml. Therefore the volume of the egg is 60 ml.