Powered by
Share this page on
Article provided by Wikipedia

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 It was superseded in 2006 by "ISO 80000-3.


Its definitions include:

Quantity Unit Remarks
Name Symbol Name Symbol Definition
(plane angle)
α, β, γ, ϑ, φ "radian rad 1 rad = 1 ​mm = 1
"degree ° 1° = ​π180 rad 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′ = (​160
"second 1″ = (​160)′
"solid angle Ω "steradian sr 1 sr = 1 ​ = 1
"length l, L "metre m The metre is the length of the path travelled by light in vacuum during a time interval of ​1299 792 458 of a second; see "speed of light
"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 ϱ
"curvature ϰ "reciprocal metre m−1 ϰ=​1ϱ
"area A "square metre The units "are (1 a = 100 m²) and "hectare (1 ha = 100 a) are used for agrarian areas.
"volume V "cubic metre
"litre L, l 1 L = 1 dm³ The capital L is preferred as the small l can be indistinguishable from the number 1 in some fonts.
"time, "time interval, duration 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 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 = 86 400 s
"angular velocity ω "radian per second rads ω=​dφdt
"angular acceleration α "radian per second squared rad α=​dωdt
"velocity v (general symbol),
v (velocity vector),
c (propagation speed of waves),
u, v, w (components of a velocity c)
"metre per second ms
"kilometre per hour kmh
"acceleration, acceleration vector a, a "metre per second squared m g = 9.80665 ​m
"acceleration of free fall, "acceleration due to gravity g

Annex A[edit]

Annex A of ISO 31-1 lists units of space and time based on the "foot, "pound, and "second.

Annex B[edit]

Annex B lists some other non-SI units of space and time, namely the "gon, "light year, "astronomical unit, "parsec, "tropical year, and "gal.

) ) WikipediaAudio is not affiliated with Wikipedia or the WikiMedia Foundation.