How can we calculate the density of a irregular solid or a liquid?

You can dip the irregular solid in a water or other suitable liquid. This is how, you can measure the volume of the solid. The mass can be measured by weighing scale. Mass/volume = density. It is easy to measure the mass and volume of the liquid. First measure the mass the container. Then add the liquid to it. You will get the mass of the liquid. Then measure the volume of the liquid. Use the above formula to calculate the density of the liquid.