You are already familiar with length and mass. Volume is how much space something takes up. The bigger the object, the more volume it has. Volume is related to length. Say, for example, you have two pipes, both of them 25 cm in diameter (25 cm wide). One pipe is 1 meter long, and the other pipe is 10 meters long. If we were to fill the pipes with water then the space that the pipe took up would be replaced with water. Which pipe will hold more water? In other words, which pipe has more volume? The second one because it has more length, and therefore more volume. Because the second pipe is ten times as long, it has ten times the volume.

Now, let's look at a different example. We have two hollow spheres - one with a radius of 5 cm and one with a radius of 10 cm (if we put them next to each other, the big one is twice as wide as the smaller one). Now, let's fill up the volume inside the sphere with water. Which sphere will hold more water, and how much more will it hold? You might want to say the big one holds twice as much water, but that is incorrect. The volume of a sphere of radius r is equal to 4/3 π r³ (remember that π = 3.14 approximately).  So the volume of a sphere depends on the radius of the sphere cubed (radius * radius * radius). Because the bigger sphere has twice the radius of the smaller sphere, it will have eight times the volume (2 cubed, 2*2*2 is 8).

The point of all this is that the relationship between size and volume depends on the geometry or shape of the object. Planets tend to be quite round, so for them, we can use the same relationship we would for a sphere.  See the below examples.

Volume of a sphere = 4/3 p r³

What is the Earth's volume assuming its radius is 6382 km or 6,382,000 m.

     Earth's volume = 4/3 x 3.14 x (6,382,000 m)³ = 1.09x10²¹ cubic meters

What is Jupiter's volume assuming its radius is 71,400,000 m (about 11 times Earth's)?

     Jupiter's volume = 4/3 x 3.14 x (71,400,000 m)³ = 1.52x10²⁴ cubic meters

How much greater is Jupiter's volume than the Earth's?

     Almost 1400 times!