what do we call the principal si units that are used to derive all other si units

For ease of understanding and convenience, 22 SI derived units have been given special names and symbols, equally shown in Table 3.

Table 3.  SI derived units with special names and symbols
	SI derived unit
Derived quantity	Name	Symbol	Expression in terms of other SI units	Expression in terms of SI base of operations units
aeroplane angle	radian (a)	rad	-	m·k-1 = one (b)
solid angle	steradian (a)	sr (c)	-	thousand2·g-2 = one (b)
frequency	hertz	Hz	-	s-1
strength	newton	N	-	m·kg·s-2
pressure, stress	pascal	Pa	Northward/mii	k-i·kg·s-2
energy, work, quantity of heat	joule	J	Northward·m	thousand2·kg·s-2
power, radiant flux	watt	Westward	J/s	m2·kg·s-3
electrical accuse, quantity of electricity	coulomb	C	-	due south·A
electric potential departure, electromotive force	volt	Five	West/A	one thousand2·kg·south-3·A-1
capacitance	farad	F	C/V	m-2·kg-1·due south4·A2
electric resistance	ohm		V/A	m2·kg·s-3·A-2
electrical conductance	siemens	Southward	A/5	m-ii·kg-ane·due souththree·Aii
magnetic flux	weber	Wb	Five·s	yard2·kg·s-ii·A-one
magnetic flux density	tesla	T	Wb/gii	kg·s-2·A-1
inductance	henry	H	Wb/A	m2·kg·southward-ii·A-2
Celsius temperature	degree Celsius	°C	-	K
luminous flux	lumen	lm	cd·sr (c)	m2·grand-2·cd = cd
illuminance	lux	60	lm/m2	mii·m-4·cd = k-2·cd
activity (of a radionuclide)	becquerel	Bq	-	s-1
absorbed dose, specific energy (imparted), kerma	gray	Gy	J/kg	grand2·s-2
dose equivalent (d)	sievert	Sv	J/kg	m2·s-2
catalytic action	katal	kat		south-one·mol
(a) The radian and steradian may be used advantageously in expressions for derived units to distinguish between quantities of a different nature but of the same dimension; some examples are given in Table iv. (b) In practice, the symbols rad and sr are used where advisable, but the derived unit "i" is generally omitted. (c) In photometry, the unit of measurement name steradian and the unit symbol sr are usually retained in expressions for derived units. (d) Other quantities expressed in sieverts are ambient dose equivalent, directional dose equivalent, personal dose equivalent, and organ equivalent dose.

For a graphical illustration of how the 22 derived units with special names and symbols given in Table three are related to the seven SI base units, meet relationships among SI units.

Note on degree Celsius. The derived unit in Table three with the special name degree Celsius and special symbol °C deserves annotate. Considering of the style temperature scales used to be defined, it remains common exercise to express a thermodynamic temperature, symbol T, in terms of its departure from the reference temperature T ₀ = 273.15 K, the water ice point. This temperature difference is called a Celsius temperature, symbol t, and is divers by the quantity equation

t= T- T ₀.

The unit of Celsius temperature is the degree Celsius, symbol °C. The numerical value of a Celsius temperature t expressed in degrees Celsius is given by

t/°C = T/K - 273.15.

It follows from the definition of t that the caste Celsius is equal in magnitude to the kelvin, which in plow implies that the numerical value of a given temperature difference or temperature interval whose value is expressed in the unit degree Celsius (°C) is equal to the numerical value of the same deviation or interval when its value is expressed in the unit kelvin (K). Thus, temperature differences or temperature intervals may be expressed in either the degree Celsius or the kelvin using the same numerical value. For example, the Celsius temperature difference t and the thermodynamic temperature difference T between the melting bespeak of gallium and the triple point of h2o may exist written equally t = 29.7546 °C = T = 29.7546 G.

The special names and symbols of the 22 SI derived units with special names and symbols given in Table 3 may themselves be included in the names and symbols of other SI derived units, as shown in Table iv.

Table iv.  Examples of SI derived units whose names and symbols include SI derived units with special names and symbols
	SI derived unit
Derived quantity	Proper noun	Symbol
dynamic viscosity	pascal 2d	Pa·s
moment of force	newton meter	Due north·one thousand
surface tension	newton per meter	N/one thousand
angular velocity	radian per 2nd	rad/south
angular acceleration	radian per 2d squared	rad/s2
heat flux density, irradiance	watt per square meter	West/k2
oestrus chapters, entropy	joule per kelvin	J/K
specific heat capacity, specific entropy	joule per kilogram kelvin	J/(kg·K)
specific energy	joule per kilogram	J/kg
thermal conductivity	watt per meter kelvin	W/(m·M)
energy density	joule per cubic meter	J/grandiii
electric field forcefulness	volt per meter	V/1000
electrical accuse density	coulomb per cubic meter	C/m3
electrical flux density	coulomb per foursquare meter	C/g2
permittivity	farad per meter	F/grand
permeability	henry per meter	H/thousand
molar free energy	joule per mole	J/mol
molar entropy, molar heat capacity	joule per mole kelvin	J/(mol·Thou)
exposure (10 and rays)	coulomb per kilogram	C/kg
absorbed dose charge per unit	grayness per second	Gy/s
radiant intensity	watt per steradian	W/sr
radiance	watt per foursquare meter steradian	W/(mtwo·sr)
catalytic (activity) concentration	katal per cubic meter	kat/miii

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Source: https://physics.nist.gov/cuu/Units/units.html

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