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