Standard Unit Conversion Tables

Question

I've been tasked with looking into some issues regarding errors with unit conversions (Meters to Feet for example). Is there a definitive source for standard conversion numbers? I would like the conversion factors to be the highest precision possible.

I know there are a number of sites out there that offer a plethora of conversions, but what I am looking for is a standard, either official or defacto to use as a baseline.

A table with 32 and 64 bit numbers would be perfect.

Answer 1

The unit definition file of GNU Units lists a large number of sources:

Most units data was drawn from

1. NIST Special Publication 811, Guide for the Use of the International System of Units (SI). Barry N. Taylor. 1995
2. CRC Handbook of Chemistry and Physics 70th edition
3. Oxford English Dictionary
4. Websters New Universal Unabridged Dictionary
5. Units of Measure by Stephen Dresner
6. A Dictionary of English Weights and Measures by Ronald Zupko
7. British Weights and Measures by Ronald Zupko
8. Realm of Measure by Isaac Asimov
9. United States standards of weights and measures, their creation and creators by Arthur H. Frazier.
10. French weights and measures before the Revolution: a dictionary of provincial and local units by Ronald Zupko
11. Weights and Measures: their ancient origins and their development in Great Britain up to AD 1855 by FG Skinner
12. The World of Measurements by H. Arthur Klein
13. For Good Measure by William Johnstone
14. NTC's Encyclopedia of International Weights and Measures by William Johnstone
15. Sizes by John Lord
16. Sizesaurus by Stephen Strauss
17. CODATA Recommended Values of Physical Constants available at http://physics.nist.gov/cuu/Constants/index.html
18. How Many? A Dictionary of Units of Measurement. Available at http://www.unc.edu/~rowlett/units/index.html
19. Numericana. http://www.numericana.com
20. UK history of measurement http://www.ukmetrication.com/history.htm
21. NIST Handbook 44, Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices. 2011
22. NIST Special Publication 447, Weights and Measures Standards of the the United States: a brief history. Lewis V. Judson. 1963; rev. 1976

For many units, the file contains the official definition, so it will be as precise as it gets. The comments often explain where that definition came from.