Measuring cylinders help in finding volume of liquids, but what of bodies with irregular shapes? This video shows how to use the water displacement method to measure the volume of bodies. A measuring cylinder or overflow vessel is used to determine two volumes - the volume before a body is immersed and the volume with the body immersed. The reasoning is that the immersed body has displaced its own volume, so by calculating the difference in volume of water, we can find the volume of the body. Once we find the mass of the body, the density can then be calculated as mass/volume. Note that this method only works of the object whose volume is to be measured completely sinks in water.
