ISO 80000-3

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ISO 80000-3:2006 is an ISO standard entitled Quantities and units – Part 3: Space and time, superseding ISO 31-1 and ISO 31-2.[1] It is a part of the group of standards called ISO/IEC 80000, which together form the International System of Quantities.

Contents list[edit]

The standard is divided into the following chapters:

  • Foreword
  • Introduction
  1. Scope
  2. Normative references
  3. Names, symbols and definitions
  • Annex A (informative) Units in the CGS system with special names
  • Annex B (informative) Units based on the foot, pound, second, and some other related units
  • Annex C (informative) Other non-SI units given for information, especially regarding the conversion factors

Names, symbols and definitions[edit]

Space and time[edit]


ISO 80000-3:2006 assigns names and symbols to quantities and units of space and time, and defines these quantities and units. For example

Units of length, area and volume[edit]
  • metre (symbol m): "length of the path travelled by light in vacuum during a time interval of 1/(299 792 458) of a second."

Other units of distance defined by the standard are the ångström (symbol Å) (10−10 m) and the nautical mile (1852 m). No symbol is given for the nautical mile.

The are (symbol a) is a unit of area equal to 100 square metres.

The litre (symbol L or l) is a unit of volume equal to 10−3 m3.

Units of angle[edit]


ISO 80000-3:2006 assigns names and symbols to quantities and units of space and time, and defines these quantities and units. For example

Units of time, speed and acceleration[edit]
  • second (symbol s): "duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom"

Other units of time defined by the standard include the minute (1 min = 60 s), the hour (1 h = 60 min) and the day (1 d = 24 h). The year is defined in an informative annex.

  • knot (symbol kn): one nautical mile per hour = 1852/3600 m/s ≈ 0.514 444 m/s.

The standard acceleration of free fall is 9.806 65 m/s2.

Logarithmic quantities and units[edit]

The bel and the neper are units of level. Level of a field quantity F is defined as ln(F/F0 ) = 20 lg(F/F0) dB. Level of a power quantity P is defined as (1/2) ln(P/P0) = 10 lg(P/P0) dB. The later ISO standard ISO 80000-1:2009 replaces the term field quantity with root-power quantity and deprecates field quantity.

Units of level defined by ISO 80000-3:2006 are

Annex A (informative)[edit]

The following CGS units are deprecated:

  • The gal (CGS unit of acceleration, equal to 1 cm/s2)

Annex B (informative)[edit]

The following non-SI units are deprecated by the standard:

  • The inch (Imperial unit of distance, equal to 25.4 mm)
  • The foot (Imperial unit of distance, equal to 12 inches)
  • The yard (Imperial unit of distance, equal to 3 feet)
  • The mile (Imperial unit of distance, equal to 1760 yards)
  • The acre (Imperial unit of area, equal to 4840 square yards)

Annex C (informative)[edit]

The following non-SI units are given for conversion. They are not deprecated by the standard

  • Units of distance: light year (the distance travelled in one year by light in vacuum; 1 l.y. ≈ 9,460 730 × 1015 m), astronomical unit (the mean distance of the Earth from the Sun, 1 ua ≈ 1,495 978 706 91(30) × 1011 m), parsec (the distance at which 1 ua subtends an angle of 1 " (second of arc); 1 pc ≈ 206 264,8 ua ≈ 30,856 78 × 1015 m)
  • Units of time: year (a), equal to either 365 days or 366 days

See also[edit]