# ISO 80000-3

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

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 centimetre–gram–second system (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

### Space and time

#### Space

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
• 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.

#### Time

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
• 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 (1 a = 365 d or 366 d) is defined in an informative annex.

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

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

### Logarithmic quantities and units

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

• neper: 1 Np = ln e = 1
• bel: 1 B = ln 10 Np ≈ 1.1512925464970228420089957273422 Np
• decibel: 1 dB = 0.1 B

## Annex A (informative)

The following CGS units are deprecated:

## Annex B (informative)

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)

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; abbreviation l.y.; 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)[2]
• Units of time: year (a), equal to either 365 days or 366 days

## References

1. ^ "ISO 80000-3:2006". International Organization for Standardization. Retrieved 20 July 2013.
2. ^ Use of symbol for the astronomical unit is inconsistent between standards and bodies, and includes, 'ua', 'au' and 'AU'.