ISO 31-1 is the part of international standard ISO 31 that defines names and symbols for quantities and units related to space and time. It was superseded in 2006 by ISO 80000-3 and again in 2019 by ISO 80000-3:2019.
Definitions
Its definitions include:
{| class="wikitable"
! colspan="2" | Quantity
! colspan="3" | Unit
! rowspan="2" width="25%"| Remarks
|-
!Name||Symbol|||Name||Symbol||Definition
|-
| rowspan="4" |angle,<br>(plane angle)
| rowspan="4" |α, β, γ, θ, φ
|radian||rad||1 rad = 1 = 1||
|-
|degree||°||1° = rad
| rowspan="3" | There is no space between the number and these superscript-style unit symbols. Decimal subdivision of degrees is preferable (i.e., 12.5° instead of 12°30′)
|-
|minute||′||1′ = ()°
|-
|second||″||1″ = ()′
|-
|solid angle||Ω||steradian||sr||1 sr = 1 = 1||
|-
|length||l, L
| rowspan="10" |metre
| rowspan="10" |m
| rowspan="10" |The metre is the length of the path travelled by light in vacuum during a time interval of of a second; see speed of light
| rowspan="10" |
|-
|breadth||b
|-
|height||h
|-
|thickness||d, δ
|-
|radius||r, R
|-
|diameter||d, D
|-
|length of path, (linear) displacement vector||s, s
|-
|distance||d, r
|-
|cartesian coordinates||x, y, z
|-
|radius of curvature||
|-
|curvature||||reciprocal metre||m<sup>−1</sup>|| ||
|-
|area||A||square metre||m<sup>2</sup>|| || The units are (1 a = 100 m<sup>2</sup>) and hectare (1 ha = 100 a) are used for agrarian areas.
|-
| rowspan="2"|volume
| rowspan="2"|V
|cubic metre||m<sup>3</sup>|| ||
|-
||litre||L, l||1 L = 1 dm<sup>3</sup> ||The capital L is preferred as the small l can be indistinguishable from the number 1 in some fonts.
|-
| rowspan="4"|time, time interval, duration
| rowspan="4"|t
|second||s||The second is the 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
| rowspan="4"|Representations of time of day are defined in ISO 8601.
|-
|minute||min||1 min = 60 s
|-
|hour||h||1 h = 60 min = 3 600 s
|-
|day||d||1 d = 24 h = 1 440 min = 86 400 s
|-
|angular velocity||ω||radian per second|||| ||ω=
|-
|angular acceleration||α||radian per second squared|||| ||α=
|-
|rowspan="2"|velocity
|rowspan="2"|v (general symbol),<br>v (velocity vector),<br>c (propagation speed of waves),<br>u, v, w (components of a velocity c)
||metre per second
|||| <!-- --> ||
|-
||kilometre per hour
| || <!-- --> ||
|-
|acceleration, acceleration vector||a, a
| rowspan="2"|metre per second squared
| rowspan="2"|
| rowspan="2"|1 g = 9.80665
| rowspan="2"|
|-
|acceleration of free fall, acceleration due to gravity||g
|}
Annex A
Annex A of ISO 31-1 lists units of space and time based on the foot, pound, and second.
Annex B
Annex B lists some other non-SI units of space and time, namely the gon, light year, astronomical unit, parsec, tropical year, and gal.