The NIST Reference on Constants, Units and Uncertainty

Units &
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Frequently Asked Questions
  1. Where can I find other, related data?
    Please see our "Links to selected scientific data."

  2. Where can I find out more about the SI and the metric system?
    Please browse our site, beginning at SI Units.

  3. Can I convert units online?
    The NIST site has an online conversion utility for energy-related quantities. Similar utilities may be found on other sites.

  4. Where can I find unit conversion factors?
    Official values of conversion factors are available from NIST in pdf form in the Appendix of Special Publication 811, which is also available free of charge by mail.

  5. Where can I find more conversion factors?
    For a very comprehensive listing of most units, see: Cardarelli, Francois. Encyclopaedia of Scientific Units, Weights and Measures. Their SI equivalences and origins. 3rd edition (Springer-Verlag, New York, London, Heidelberg, 2003), 872 pages, ISBN 1-85233-682-X; Hardcover.

  6. Can I print a list of all the constants?
    Yes, as a pdf. Viewing this file will require an Adobe Acrobat viewer and/or plug-in. Go to our main constants page, choose "Find value in category (via Table - PDF)" and click "All values." Or click here.

  7. What is the proper way of writing...?
    We have summarized most of the rules and style conventions for writing SI units via a checklist designed to help authors review the conformity of their manuscripts with proper SI usage and the basic principles concerning quantities and units.

  8. May we link to your site?
    Absolutely, although we would prefer you to link to one of our home pages: Values of the constants and related information, Searchable bibliography on the constants, In-depth information on the SI, the modern metric system, or Guidelines for the expression of uncertainty in measurement. Or our main home page.

  9. I think I have found an error.
    Please send it to us. Thank you.


Last update: November 2004

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