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 It was superseded in 2006 by ISO 80000-3.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 | |
angle, (plane angle) |
α, β, γ, θ, φ | radian | rad | 1 rad = 1 m⁄m = 1 | |
degree | ° | 1° = π⁄180 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′ = (1⁄60)° | |||
second | ″ | 1″ = (1⁄60)′ | |||
solid angle | Ω | steradian | sr | 1 sr = 1 m^{2}⁄m^{2} = 1 | |
length | l, L | metre | m | The metre is the length of the path travelled by light in vacuum during a time interval of 1⁄299 792 458 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} | ||
area | A | square metre | m^{2} | The units are (1 a = 100 m^{2}) and hectare (1 ha = 100 a) are used for agrarian areas. | |
volume | V | cubic metre | m^{3} | ||
litre | L, l | 1 L = 1 dm^{3} | 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 = 1 440 min = 86 400 s | |||
angular velocity | ω | radian per second | rad⁄s | ω=dφ⁄dt | |
angular acceleration | α | radian per second squared | rad⁄s^{2} | α=dω⁄dt | |
velocity | v (general symbol), v (velocity vector), c (propagation speed of waves), u, v, w (components of a velocity c) |
metre per second | m⁄s | ||
kilometre per hour | km⁄h | ||||
acceleration, acceleration vector | a, a | metre per second squared | m⁄s^{2} | 1 g = 9.80665 m⁄s^{2} | |
acceleration of free fall, acceleration due to gravity | g |
Annex A of ISO 31-1 lists units of space and time based on the foot, pound, and second.
Annex B lists some other non-SI units of space and time, namely the gon, light year, astronomical unit, parsec, tropical year, and gal.