How to Measure the Thickness of a Sheet of Paper
The thickness of a single sheet of paper (known in the paper industry as its "caliper") is not something you can easily measure directly using a simple ruler. However, if you have a standard ream of paper (500 sheets) or a stack of clean paper with a known number of sheets, you can very accurately calculate the paper's thickness with nothing more than a ruler calibrated to at least millimeters, sixteenths an inch, or a finer scale. Knowing the thickness of a sheet of paper can also help you estimate the number of sheets in a stack, provided the paper is a type whose caliper you have measured before.
First make sure all the paper in the stack is clean and free from marks or wrinkles that will affect the thickness calculation. Justify the edges of the paper so that you have four flat sides to measure against. Gently pressing down on the stack with your palm, measure the height of the stack of paper as accurately as possible.
Now divide this measurement by the number of pages in the stack. The final number is the thickness of the paper. Though the method is simple, it's important that you make your measurements as accurately as possible and to count the exact number of pages. If you are off by a tenth or hundredth, the final calculated answer will be quite different from the actual thickness. The more pieces of paper in a stack, the more accurate the calculation.
A stack of 700 sheets of copy paper has a height of 6.8 centimeters. Since 6.8/700 = 0.009714, each sheet of paper in the stack has a thickness of 0.009714 centimeters. This is equivalent to 0.09714 millimeters or 97.14 microns.
A ream of loose leaf notebook paper has a thickness of 1 and 15/16 inches. For this calculation you must know that a ream is 500 sheets and the decimal equivalent of 1 and 15/16 inches is 1.9375 inches. Since 1.9375/500 = 0.003875, each sheet is 0.003875 inches thick, or 3.875 mils thick. (One mil = one thousandth of an inch.)
Some commonly used units of measurement for objects that are very thin are microns (aka mircometers) and mils. Microns are metric units and 1 micron or 1 µm = 1/1000 mm, or equivalently 1/1000000 m. Mils (also called thou) are imperial units and 1 mil = 1/1000 inch. Equivalently, 1 mil = 25.4 microns, so a micron is smaller than a mil.
A book has 1118 pages and the compressed height of the pages between the front and back covers is 6.75 cm. Using the technique above, the thickness of a single page is 6.75/1118 = 0.006038 cm, or equivalently, 0.06038 mm.
When using this division method, the number of pages is the number of individual sheets of paper bound in the book. You don't want to use the double-sided page number counts. For example, if the last page of the book is numbered 396, the number of individual sheets is half that number, 198. Also, make sure you compress the pages when measuring the height so you don't count the thickness of layers of air between the sheets.
Difference Between Thickness and Weight
Paper quality is usually given as weight, which is not the same as thickness. In the paper industry, paper weight or paper density or grammage is the weight of paper per unit of area. For instance, office paper has a typical grammage of 80 grams per square meter. There is no simple conversion between grammage and actual thickness as a paper's composition must be taken into account.
Suppose you already know that a certain type of paper is about 103.4 microns thick. You have a stack of this paper that is 15.8 cm tall. About how many sheets are in this stack?
First we convert both the thickness of the paper and the height of the stack to millimeters. This gives us a thickness of 0.1034 mm and a paper stack height of 158 mm. Now we divide 158 by 0.1034, which gives us
158/0.1034 = 1528.0464
So this stack contains approximately 1528 sheets of paper, assuming the paper thickness measurement is accurate.