The density of an object measures how much the object weights relative to the amount of space the object takes up. Dense objects have a higher weight per unit of volume; less dense objects weigh less per unit of volume. In the standard system, density is usually measured in kilograms per cubic meter, kilograms per cubic centimeter or grams per cubic centimeter. In the U.S. system, density is usually measured in pounds per cubic inch or pounds per cubic foot. In order to calculate the mass, you need to know the density and the volume.
Determine the density of the object you want to calculate the mass of. For example, the density of copper equals 0.324 lbs per cubic inch.
Determine the volume of the item you want to determine the mass of. If the item is a regular shape, such as a rectangular prism, you can measure the dimensions and the use the volume formula, such as length times width times height, to calculate the volume. For example, if you have a copper rectangular prism that measures 4-by-6-by-2 inches, the volume would be 48 cubic inches.
If the item is irregular, you can fill a beaker halfway with a water, record the volume and place the item in the water. Subtract the initial volume from the final volume to determine the volume of the item.
Multiply the volume of the item by the density of the material. For example, if you have 48 cubic inches of copper and the density of copper is 0.324 lbs per cubic inch, the mass of the object would be 15.552 pounds.