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 It was superseded in 2006 by ISO 80000-3 and again in 2019 by ISO 80000-3:2019.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:
Quantity Unit RemarksNameSymbolNameSymbolDefinitionangle,(plane angle)α, β, γ, θ, φradianrad1 rad = 1 = 1degree°1° = 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′ = ()°second″1″ = ()′solid angleΩsteradiansr1 sr = 1 = 1lengthl, LmetremThe metre is the length of the path travelled by light in vacuum during a time interval of of a second; see speed of lightbreadthbheighththicknessd, δradiusr, Rdiameterd, Dlength of path, (linear) displacement vectors, sdistanced, rcartesian coordinatesx, y, zradius of curvaturecurvaturereciprocal metrem−1 areaAsquare metrem2 The units are (1 a = 100 m2) and hectare (1 ha = 100 a) are used for agrarian areas.volumeVcubic metrem3 litreL, l1 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, durationtsecondsThe 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 atomRepresentations of time of day are defined in ISO 8601.minutemin1 min = 60 shourh1 h = 60 min = 3 600 sdayd1 d = 24 h = 1 440 min = 86 400 sangular velocityωradian per second ω=angular accelerationαradian per second squared α=velocityv (general symbol),v (velocity vector),c (propagation speed of waves),u, v, w (components of a velocity c)metre per second kilometre per hour acceleration, acceleration vectora, ametre per second squared1 g = 9.80665 acceleration of free fall, acceleration due to gravityg
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.
References