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Unit Conversion

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 - 2014 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 HB 133 Appendix E - 2014 provides unit conversion factor tables for the benefit of those requiring an reference when checking the net contents of packaged goods.

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


  • "If you have an amount of unit of A, how much is that in unit B?"
  • Dimensional Analysis
  • Principle - quantities defined as equalities

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  • Conversion Factor: an expression for the relationship between units.

4 Steps


  • 1. What do you have?
    • Starting Units
  • 2. What do you want?
    • Desired Units
  • 3. Identify Conversion Factor(s)
    • Ratio or Linking Units
  • 4. Cancel Units Where You Can and Do the Math

Setting Up the Problem

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Example


Convert 5 m to ? cm

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