How Many? A Dictionary of Units of Measurement
© Russ Rowlett and the University of North Carolina at Chapel Hill

Table of Contents
About the Dictionary
Using the Dictionary

Links to Related Sites

Basic Sources

U. S. Metric Association. The Association, founded in 1916, promotes use and understanding of the SI and the metric system in the United States. It publishes a variety of useful guides and educational aids, some of which are available online. Its Chronology of the SI Metric System is a brief outline of metric history, and its Correct SI Metric Usage is a guide to proper style in using metric units in papers and publications.

NIST Metric Program. NIST is the National Institute of Standards and Technology, formerly known as the National Bureau of Standards, an agency of the U.S. Department of Commerce. NIST is concerned very broadly with establishing and maintaining technical and scientific standards for industry and research. The Metric Program is responsible for encouraging broad use of the metric system and for coordinating the plans of federal agencies to convert their measurements to metric units. Its brochure, The United States and the Metric System, provides history and background for the metrication effort. It has published a Metric Style Guide for the News Media with details on how to use metric units correctly in text.

NIST Fundamental Physical Constants. From time to time the values of fundamental constants (mass of the electron, Planck's constant, etc.) are revised to reflect recent experimental measurements. Since the various constants are interrelated, it is necessary to revise all of them at once. The last general revision was in 2002; the new values differ slightly from those found in many standard textbooks and other references. Fundamental physical constants appear in this dictionary only if they are used as units of measurement.

NIST Physics Laboratory Publications. At this web site you can read or download (in Adobe Acrobat format) two important official publications:

Bureau International des Poids et Mésures. Home page for the international organization that maintains the SI. The same information is provided in French and in English. Here you can read or download the official specifications of the International System of Units in a document known informally as the SI Brochure.

The Modern Metric System ( A concise and useful summary of the metric system by Chris Kaese.

UK Metrication Association. The association promotes metrication in Britain; its site includes a useful history of the metrication effort.

British Weights and Measures Association. The association opposes compulsory metrication and promotes continued use of the traditional British units.

Other Sites with Units Data

A Dictionary of Units. Originally written by Frank Tapson of the University of Exeter in Britain, this useful site is now maintained by Cleve Books. It includes a long list of very carefully computed and precise factors for converting between units as well as links to calculators that will do this work for you.

ASCE Committee on Metrication. The American Society of Civil Engineers has a very complete site on metric conversion. It includes background and discussion of the issues involved. There's also a huge table of conversion factors suitable for converting almost anything into metric units.

Metric prefixes. This page, by Bob Bruner of the University of California, has some excellent "sense of scale" examples. Did you know that a zettameter is approximately the radius of the Milky Way galaxy? Or that the age of the Universe is about half an exasecond?

Metric Units Galore. A huge compendium, by Olle Järnefors, of metric units current and obsolete, with their symbols. A valuable reference.

Unit Converter Sites

Conversion Factors. From Process Associates of America, a chemical engineering organization. Very useful modules provide conversion factors for a broad range of engineering units, with a high degree of precision.

Conversion of Units. This site, posted by the Chemistry Department of the Free University of Berlin (Germany), provides fast and accurate conversion between dozens of units of all kinds.

Online Metric Converter from Science Made Simple. Handy, easy to use conversions for most of the common units. A nice feature is that you can work with only the common units, or you can expand the menus to include less-familar units as well. is a web-based conversion site which will perform almost any imaginable unit conversion. It is a service of Entisoft Units, a shareware program for units conversion. Site includes a huge listing of units with standard equivalents.

MegaConverter. A fancy commercial site, featuring a collection of conversion modules which instantly convert between units of measurement. Seriously cool, but it doesn't cover all the categories of units (yet, anyway).

Metric Typographic Units. A thorough discussion of traditional and metric units in typesetting and page layout, by Markus Kuhn.

Historic Units

15 USC Chapter 6. Posted by the Cornell University Law School, this is the law concerning weights and measures in the United States.

Surveying Units and Terms. Posted by Direct Line Software, which serves surveyors and geneologists struggling with old U.S. deeds and land grants, this page includes traditional units of land measurement in British, French, and Spanish North America.

Measures from Antiquity and the Bible. An interesting site posted by Jack Proot on America Online. Discusses length measurement in Egypt, Mesopotamia, Persia, Greece, and Rome. Only a handful of these units are included in this work. (Proot also has a page on Anglo-Saxon Weights and Measures, nearly all of which are also listed in this dictionary.)

Old Units of Length. A good, concise discussion by J.B. Calvert of the University of Denver. Includes information on Greek and Roman measurements.

Greek and Roman Weights, Measures, and Currency. This useful site is posted by Prof. John Porter of the University of Saskatchewan.

Old Swedish Units. Olle Järnefors provides this description of Swedish units and how they have changed over time. Before adopting the metric system, Swedes used a decimalized version of their customary units from 1855 to 1889.

Foundation metrology. Interesting research on ancient Egyptian units and their relationship to other ancient measurement systems.

Light Units

The Unit of Luminous Intensity: the Candela. A nice discussion of the various light units, including the lumen and lux as well as the candela, posted by Electro Optical Industries, Inc.

Time and Calendar Units

Time Zone Converter. This commercial site provides the correct local time right now in every country and most major cities of the world.

Today's Calendar and Clock Page. THE site for information on all the world's calendars and how to convert between them. An invaluable resource, from Will Linden.

International Standard Date and Time Notation. A thorough discussion of the ISO 8601 standard and other notations in use, from Markus Kuhn.

Animal Group Names

Animal Collectives. You know, a pod of whales, a gaggle of geese, etc. These are not units of measurement (because they don't refer to a specific number), but people ask about them. This British source has the largest collection of these names I have seen.


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All material in this folder is copyright © 2004 by Russ Rowlett and the University of North Carolina at Chapel Hill. Permission is granted for personal use and for use by individual teachers in conducting their own classes. All other rights reserved. You are welcome to make links to this page, but please do not copy the contents of any page in this folder to another site. The material at this site will be updated from time to time.

Checked October 26, 2004