Density is the mass of a substance in each unit of volume. It tells you how tightly the mass is packed. The equation is density = mass ÷ volume. With mass in kilograms (kg) and volume in cubic metres (m3), density is in kilograms per cubic metre (kg/m3). Water has a density of 1000 kg/m3. A density in g/cm3 is 1000 times smaller than the same density in kg/m3, so 1 g/cm3 equals 1000 kg/m3.
To find the density of a regular solid block, measure its mass with a balance. Then measure its length, width and height with a ruler and multiply them together to get the volume.
For an irregular solid, lower it into a eureka can full of water. The water it displaces is collected in a measuring cylinder, and the volume of the displaced water equals the volume of the object. Example: a block of mass 0.40 kg and volume 0.0005 m3 has density 0.40 ÷ 0.0005 = 800 kg/m3.
