Unit conversion is a multi-step process that involves multiplication or division by a numerical factor, selection of the correct number of significant digits, and rounding. This multi-step process is presented in NIST SP 1038 - 2006 (Section 4.4), including a rounding procedure for technical documents, specifications, and other applications such packaged goods in the commercial marketplace and temperature. Common conversion factors are also listed (Section 5).
NIST HB 44 – Appendix C - 2013 provides several convenient conversion factor tables for length, area, volume (dry and liquid measure), and mass using SI (metric system) and U.S. customary units, including notes on British measurement units.
NIST SP 811 – Appendix B - 2008 provides guidance on the use of conversion factors which are expressed using scientific notation (listed both alphabetically and by topic areas) and rules for rounding numbers and converted numerical values of quantities.
Unit Conversion Example
Setting Up the Problem