The thickness of an object is defined as the smallest of three descriptive measurements: height, width and length. If you're dealing with a rectangular prism, and if its volume and the area of one side are provided, you can use those two measurements to calculate its thickness. For example, if you know the volume of the slab of cement that forms your driveway and the driveway's surface area, you can calculate the slab's thickness. Just make sure that the object's area and volume are given in the same units of measure.
TL;DR (Too Long; Didn't Read)
To find an object's thickness, divide its volume by the area of one side:
volume ÷ area of side = thickness
Check Units of Measure
Double-check that the area of one of the object's sides and volume are measured in the same units. For example, if the area is in inches squared and the volume is in feet cubed, the volume would need to be converted to inches cubed.
Divide Volume by Area
Divide the volume of the object by the area of one of the sides to attain the thickness. Suppose that the side area was 40 square inches and the volume was 80 cubic inches. You would then calculate:
80 in3 ÷ 40 in2 = 2 in
The result, 2 inches, is your value for the thickness of the object.
Use Linear Units
Place the correct units onto the thickness measurement as it is only one-dimensional. For example, if the area was square inches, the units of the objects thickness would be (linear) inches. In the example, the thickness would be 2 inches.