sv3rev 12026-03-17INTERNATIONAL BUREAU OF WEIGHTS AND MEASURES (BIPM); The International System of Units (SI) - 9th editon 2019
second
0112/2///62720#UAA972
SI unit of time defined by taking the fixed numerical value of the caesium frequency, ∆νCs, the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom, to be 9 192 631 770 when expressed in the unit Hz, which is equal to s−1
unitAll properties21#
- Version
- 3
- Revision
- 1
- Preferred name
- second
- Short name
- s
- Definition
- SI unit of time defined by taking the fixed numerical value of the caesium frequency, ∆νCs, the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom, to be 9 192 631 770 when expressed in the unit Hz, which is equal to s−1
- Definition source
- INTERNATIONAL BUREAU OF WEIGHTS AND MEASURES (BIPM); The International System of Units (SI) - 9th editon 2019
- Note
- Base unit of the International System of Units (SI)
- Unit structure
- s¹
- Unit in text
- second
- Unit in SGML/XML
Structured markup (math)(121 chars)
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block"> <!-- UAA972 --> <mi mathvariant="normal">s</mi> </math>
- UN/ECE code
- SEC
- Unit conversion
Structured markup (UnitsML)(501 chars)
<UnitsML xmlns="https://schema.unitsml.org/unitsml/1.0"><Unit xml:id="0112/2///62720#UAA972"><Conversions><Float64ConversionFrom xml:id="UAA972_from_UAA972" initialUnit="0112/2///62720#UAA972" multiplicand="1" divisor="1" exact="true" /></Conversions></Unit><Unit xml:id="https://si-digital-framework.org/SI/units/second"><Conversions><Float64ConversionFrom xml:id="SI::second_from_UAA972" initialUnit="0112/2///62720#UAA972" multiplicand="1" divisor="1" exact="true" /></Conversions></Unit></UnitsML>
- Responsible committee
- IEC/SC 3D
- Publisher
- IEC
- Published in
- IEC 62720
- Status level
- Standard
- Version release date
- 2026-03-17
- Revision release date
- 2026-03-17
- Version initiation date
- 2026-03-17
- Change request ID
- C00192