A sheet of ordinary office or copier paper is about 0.1 millimeters thick, a tenth of a millimeter. That is the distance through the sheet, from one face to the other. Other papers are thinner or thicker, from newsprint to card.

Size

The U.S. National Nanotechnology Initiative gives the thickness of a sheet of paper as about 100,000 nanometers, which is 0.1 millimeters. A nanometer is a millionth of a millimeter.

The U.S. government's paper standards list plain copier paper at 4 mils thick on average. A mil is a thousandth of an inch, exactly 25.4 micrometers, so 4 mils is 0.1016 millimeters. A micrometer is a thousandth of a millimeter.

Paper comes in many grades, and their thickness varies. In the same standards, newsprint is 0.07–0.08 millimeters thick, and heavier copier papers are 0.11–0.13 millimeters. Index paper, used for index cards, is 0.19–0.34 millimeters. Paper standards call a sheet's thickness its caliper.

Size comparisons

About 10 sheets stacked together make a stack 1 millimeter thick, the smallest division on a metric ruler.
A stack of 500 sheets of copier paper is about 5 centimeters (2 inches) thick.
A sheet of copier paper is about as thick as a human hair is wide, about 0.1 millimeters.
A human egg cell, or ovum, is about 0.12 millimeters across, a little more than the thickness of a sheet.
Folding a sheet in half doubles its thickness. Seven folds would make 128 layers, about 1.3 centimeters (half an inch) thick. If a sheet could be folded 42 times, it would be about 440,000 kilometers (270,000 miles) thick. That is more than the average distance from Earth to the Moon, 384,400 kilometers (238,900 miles).

Weight and thickness

The government standards describe most grades of paper by weight rather than thickness. Only a few grades, such as some coated cover papers, are sold by thickness.

In the United States, a paper's basis weight is the weight in pounds of 500 sheets of the grade's basic size. Plain copier paper has a basis weight of 20 pounds: 500 sheets measuring 17 by 22 inches weigh 20 pounds. In metric terms that is about 75 grams per square meter.

Heavier paper is usually thicker. The government standards list 20-, 24- and 28-pound copier papers at 4.0, 4.5 and 5.0 mils. Weight is not the whole story, though. Cover papers that all have a basis weight of 65 pounds range from 5.7 to 8.1 mils thick, depending on the grade and how its surface is finished.

The standards also limit how much the thickness may vary. Uncoated paper for printing books, for example, must not vary by more than about 10 micrometers (0.0004 inches) from one edge to the other.

Sources

Just How Small Is "Nano"?. National Nanotechnology Coordination Office.
Government Paper Specification Standards No. 13. U.S. Government Publishing Office, 2019.
NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically. National Institute of Standards and Technology.
Oocyte diameter predicts the maturation rate of human immature oocytes collected ex vivo. Pors et al., Journal of Assisted Reproduction and Genetics, 2022.
Moon Fact Sheet. NASA, 2024.

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