Electronics World articles Popular Electronics articles QST articles Radio & TV News articles Radio-Craft articles Radio-Electronics articles Short Wave Craft articles Wireless World articles Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors Engineer Jobs LinkedIn Crosswords Engineering Humor Kirt's Cogitations RF Engineering Quizzes Notable Quotes App Notes Calculators Education Engineering magazine articles Engineering software Engineering smorgasbord RF Cafe Archives RF Cascade Workbook 2018 RF Stencils for Visio RF & EE Shapes for Word Advertising RF Cafe Homepage Thank you for visiting RF Cafe!
Innovative Power Products Resistors

SI Base Units & Derived Units
The data presented here is derived from publications of NIST, so it is in the public domain. However, this HTML implementation is not in the public domain. It is provided to make for easier access.

SI Base Units
The SI is founded on seven SI base units for seven base quantities assumed to be mutually independent, as given in Table 1.

Table 1.  SI base units
SI base unit
Base quantity Name Symbol
length meter m
mass kilogram      kg
time second s
electric current ampere A
thermodynamic temperature      kelvin K
amount of substance mole mol
luminous intensity candela cd

For detailed information on the SI base units, see Definitions of the SI base units and their Historical context.

SI Derived Units

Other quantities, called derived quantities, are defined in terms of the seven base quantities via a system of quantity equations. The SI derived units for these derived quantities are obtained from these equations and the seven SI base units. Examples of such SI derived units are given in Table 2, where it should be noted that the symbol 1 for quantities of dimension 1 such as mass fraction is generally omitted.

Table 2.  Examples of SI derived units
SI derived unit
Derived quantity Name Symbol
area square meter m2
volume cubic meter m3
speed, velocity meter per second m/s
acceleration meter per second squared  m/s2
wave number reciprocal meter m-1
mass density kilogram per cubic meter kg/m3
specific volume cubic meter per kilogram m3/kg
current density ampere per square meter A/m2
magnetic field strength  ampere per meter A/m
amount-of-substance concentration mole per cubic meter mol/m3
luminance candela per square meter cd/m2
mass fraction kilogram per kilogram, which may be represented by the number 1 kg/kg = 1


For ease of understanding and convenience, 22 SI derived units have been given special names and symbols, as 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 units
plane angle radian (a) rad   - m·m-1 = 1 (b)
solid angle steradian (a) sr (c)   - m2·m-2 = 1 (b)
frequency hertz Hz   - s-1
force newton N   - m·kg·s-2
pressure, stress pascal Pa N/m2 m-1·kg·s-2
energy, work, quantity of heat  joule J N·m m2·kg·s-2
power, radiant flux watt W J/s m2·kg·s-3
electric charge, quantity of electricity coulomb C   - s·A
electric potential difference,
electromotive force		 volt V W/A m2·kg·s-3·A-1
capacitance farad F C/V m-2·kg-1·s4·A2
electric resistance ohm Omega V/A m2·kg·s-3·A-2
electric conductance siemens S A/V m-2·kg-1·s3·A2
magnetic flux weber Wb V·s m2·kg·s-2·A-1
magnetic flux density tesla T Wb/m2 kg·s-2·A-1
inductance henry H Wb/A m2·kg·s-2·A-2
Celsius temperature degree Celsius °C   - K
luminous flux lumen lm cd·sr (c) m2·m-2·cd = cd
illuminance lux lx lm/m2 m2·m-4·cd = m-2·cd
activity (of a radionuclide) becquerel Bq   - s-1
absorbed dose, specific energy (imparted), kerma gray Gy J/kg m2·s-2
dose equivalent (d) sievert Sv J/kg m2·s-2
catalytic activity katal kat s-1·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 4.
(b) In practice, the symbols rad and sr are used where appropriate, but the derived unit "1" is generally omitted.
(c) In photometry, the unit 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 3 are related to the seven SI base units, see relationships among SI units.

Note on degree Celsius. The derived unit in Table 3 with the special name degree Celsius and special symbol °C deserves comment. Because of the way temperature scales used to be defined, it remains common practice to express a thermodynamic temperature, symbol T, in terms of its difference from the reference temperature T0 = 273.15 K, the ice point. This temperature difference is called a Celsius temperature, symbol t, and is defined by the quantity equation

t= T- T0.

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 degree Celsius is equal in magnitude to the kelvin, which in turn 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 difference 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 Deltat and the thermodynamic temperature difference DeltaT between the melting point of gallium and the triple point of water may be written as Deltat = 29.7546 °C = DeltaT = 29.7546 K.

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 4.

Table 4.  Examples of SI derived units whose names and symbols include SI derived units with special names and symbols
SI derived unit
Derived quantity Name Symbol
dynamic viscosity pascal second Pa·s
moment of force newton meter N·m
surface tension newton per meter N/m
angular velocity radian per second rad/s
angular acceleration radian per second squared rad/s2
heat flux density, irradiance watt per square meter W/m2
heat capacity, 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·K)
energy density joule per cubic meter J/m3
electric field strength volt per meter V/m
electric charge density coulomb per cubic meter C/m3
electric flux density coulomb per square meter C/m2
permittivity farad per meter F/m
permeability henry per meter H/m
molar energy joule per mole J/mol
molar entropy, molar heat capacity joule per mole kelvin J/(mol·K)
exposure (x and gamma rays) coulomb per kilogram C/kg
absorbed dose rate gray per second Gy/s
radiant intensity watt per steradian W/sr
radiance watt per square meter steradian W/(m2·sr)
catalytic (activity) concentration katal per cubic meter kat/m3
RF Cascade Workbook 2018 by RF Cafe
RF Electronics Symbols for Office by RF Cafe
RF Electronics Shapes for Office by RF Cafe
LadyBug Technologies LB5944A RF Power Sensor - RF Cafe Berkeley Nucleonics Model 855B Signal Generator - RF Cafe
About RF Cafe
Kirt Blattenberger - RF Cafe Webmaster
Copyright: 1996 - 2024
Webmaster:
    Kirt Blattenberger,
    BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while typing up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

My Hobby Website:  AirplanesAndRockets.com

spacer

Please Support RF Cafe by purchasing my  ridiculously low−priced products, all of which I created.

These Are Available for Free