First, you need to determine the shape of the object to know which formula to use.
In general, you'll start with three numbers because you are measuring three-dimensional objects.
When you use a formula for an area the number gets squared. For volume, the number gets cubed.
Cube or Rectangle
To calculate the volume of a box you multiply the length, width, and height.
For a cube they are all the same, so you can multiply the single number to the third power.
Using the formula above, your cube would have a height, length, and width of 2 inches. While the total volume of the cube is 8.
Ball or Cylinder
How to calculate the volume of a circle shaped object starts with finding the radius.
For a ball, you need to multiply the radius by (pi) and 4/3.
For a cylinder, you need to include the height of the cylinder. Think of a cylinder as two circles with space in between.
Sphere Volume= 4/3 x (pi) x radius to the power of 3
Cylinder volume= height x (pi) x radius to the power of 2
Cone
The volume of a cone gets more complicated.
Cone volume = 1/3 x (pi) x height x radius to the second power.
The radius is a straight line from the center to the outer edge of the widest part of the cone.
Odd Shapes
The best way to tackle calculating an odd shape is to break it down into simpler shapes. Start by breaking the shape down into a cube, cylinder, or sphere. Once you figured out the volume for the individual shapes you can add the individual volumes.