How To Measure The Volume Of A Solid Object

If you have an object with a standard geometric shape, such as a cube or a sphere, you can calculate its volume by measuring its dimensions and using the relevant mathematical formula. For example, if you measure the length of one side of a cube (L), the volume of the cube is L³. The volume of a sphere would be:

\(V=\frac{4}{3}\pi r^3\)

What do you do with an irregular object, though, such as a pen or a rock? The Greek philosopher Archimedes was faced with this problem when he was asked to find the density of the king's crown. To determine its density, he had to know its volume, and his "Eureka" moment occurred when he realized he could do it by immersing the crown in water and measuring the amount of water that was displaced. The displacement method is still the standard way to determine the volume of an irregularly shaped object.

1. Find a Suitable Container

Look for a container large enough to hold the object. It's best to use a container with a regular shape, such as a cylinder or a box, because you'll need to calculate its volume. If you don't have a regular container, you can always fill it to the brim with water, catch the water that overflows when you immerse the object you're measuring and transfer the water to a graduated vessel.

2. Fill the Container with Water

Add at least enough water to allow you to completely immerse the object. If you aren't using a graduated container, mark the water level on the side of the container.

3. Immerse the Object and Note the Change in Water Level

Read the new level on the scale if you use a graduated vessel. Subtract the old level from this one to get the change in level.

If you don't use a graduated container, make a new mark on the container. Subtract the height of the original mark from the height of the new one to get the change in water level.

4. Calculate the Volume of Water Displacement

Read the volume levels if you use a graduated container, but if you use an ungraduated container, you'll have to calculate the volume. The calculation depends on the shape of the container.

​Cylindrical Container:​ Measure the radius of the container opening (r) and calculate volume of displaced water using this formula:

\(V=\pi r^2 \times \text{ change in water depth}\)

​Rectangular Container:​ Measure the length (L) and width (W) of the container opening. The volume of displaced water is:

\(V = L\times W\times \text{ change in water depth}\)

You may be measuring the volume of a copper penny or a silver statue. Both of these have known densities that you can look up. If you know the density of the material from which the object is made, you can find the volume simply by weighing the object. Since density = mass ÷ volume; volume = mass ÷ density.

​Example:​ A silver statue weighs 10 kilograms. Since the density of silver is 10,490 kg/m³, the volume is:

\(V=\frac{10}{10,490}=0.00095\text{ m}^3\)

1 cubic meter equals 1,000 liters, so this equals 0.95 liters or 0.25 U.S. gallons.