Appendix V: Units

As described in the Units, the specification of units SHOULD follow the International System of Units (SI, abbreviated from the French Système international (d’unités)).

The CMIXF-12 convention for encoding units is RECOMMENDED to achieve maximum portability and limited variability of representation. If a CMIXF-12 representation of a unit is not possible, the unit can be declared as custom units and defined in an accompanying JSON file, as described in the units section. Earlier versions of the BIDS standard listed the following Unicode symbols, and these are still included for backwards compatibility:

1. U+03BC (μ) or U+00B5 (µ)

2. U+03A9 (Ω) or U+2126 (Ω)

3. U+00B0 (°)

Note that for the first two entries in this list, two characters are permissible for each, but the first character in each entry is preferred, per Unicode rules (see the section on “Duplicated Characters” on page 11 in the unicode report).

It is RECOMMENDED that units be CMIXF-12 compliant or among these five Unicode characters. Please note the appropriate upper- or lower- casing when using CMIXF-12.

For cases that are unspecified by this appendix or the units section, the CMIXF-12 convention applies.

You can use the cmixf Python package to check whether your formatting is compliant.

Examples for CMIXF-12 (including the five unicode symbols mentioned above):

1. Different formatting of “micro Volts”:

   1. RECOMMENDED: uV or µV

   2. NOT RECOMMENDED: microV, µvolt or 1e-6V

2. Combinations of units:

   1. RECOMMENDED: V/us for the Slew rate

   2. NOT RECOMMENDED: volts per microsecond

Unit table

Unit name	Unit symbol	Quantity name
metre	m	length
kilogram	kg	mass
litre (liter)	L	volume
second	s	time
ampere	A	electric current
kelvin	K	thermodynamic temperature
mole	mol	amount of substance
candela	cd	luminous intensity
radian	rad	angle
steradian	sr	solid angle
hertz	Hz	frequency
newton	N	force, weight
pascal	Pa	pressure, stress
joule	J	energy, work, heat
watt	W	power, radiant flux
coulomb	C	electric charge or quantity of electricity
volt	V	voltage (electrical potential), emf
farad	F	capacitance
ohm	Ohm	resistance, impedance, reactance
siemens	S	electrical conductance
weber	Wb	magnetic flux
tesla	T	magnetic flux density
henry	H	inductance
degree Celsius	oC	temperature relative to 273.15 K
lumen	lm	luminous flux
lux	lx	illuminance
becquerel	Bq	radioactivity (decays per unit time)
gray	Gy	absorbed dose (of ionizing radiation)
sievert	Sv	equivalent dose (of ionizing radiation)
katal	kat	catalytic activity

Prefixes

Multiples

Prefix name	Prefix symbol	Factor
deca	da	101
hecto	h	102
kilo	k	103
mega	M	106
giga	G	109
tera	T	1012
peta	P	1015
exa	E	1018
zetta	Z	1021
yotta	Y	1024

Submultiples

Prefix name	Prefix symbol	Factor
deci	d	10-1
centi	c	10-2
milli	m	10-3
micro	u	10-6
nano	n	10-9
pico	p	10-12
femto	f	10-15
atto	a	10-18
zepto	z	10-21
yocto	y	10-24