Last Updated On
Wednesday, May 31, 2023
Measurement
SI defining constants
Symbol
Defining constant
Exact value
ΔνCs
hyperfine transition frequency of Cs
9192631770 Hz
c
speed of light
299792458 m/s
h
Planck constant
6.62607015*10^-34 J*Hz^-1
e
elementary charge
1.602176634*10^-19 C
k
Boltzman constant
1.380649*10^-23 J/K
NA
Avogadro constant
6.02214076*10^23 mol^-1
luminous efficacy of 540 THz radiation
683 Im/W
SI base units
Name
Quantity
s
second
time
m
metre
length
kg
kilogram
mass
A
ampere
electric current
K
kelvin
thermodynamic temperature
mol
mole
amount of substance
cd
candela
luminous intensity
SI derived units with special names and symbols
In SI base units
In other SI units
radian
rad
plane angle
m/m
1
steradian
sr
solid angle
m^2/m^2
hertz
Hz
frequency
s^-1
newton
N
force, weight
kg*m*s^-2
pascal
Pa
pressure, stress
kg*m^-1*s^-2
N/m^2=J/m^3
joule
J
energy, work, heat
kg*m^2*s^-2
N/m=Pa*m^3
watt
W
power, radiant flux
kg*m^2*s^-3
J/s
coulomb
C
electric charge
s*A
volt
V
electric potential, voltage, emf
kg*m^2*s^-3*A^-1
W/A=J/C
farad
F
capacitance
kg^-1*m^-2*s^4*A^2
C/V=C^2/J
ohm
Ω
resistance, impedance, reactance
kg*m^2*s^-3*A^-2
V/A=J*s/C^2
siemens
S
electrical conductance
kg^-1*m^-2*s^3*A^2
Ω^-1
weber
Wb
magnetic flux
kg*m^2*s^-2*A^-1
V*s
tesla
T
magnetic flux density
kg*s^-2*A^-1
Wb/m^2
henry
H
inductance
kg*m^2*s*-2*A^-2
Wb/A
Celsius
°C
temperature relative to 273.15 K
lumen
lm
luminous flux
cd*sr
lux
lx
luminance
cd*sr*m^-2
lm/m^2
becquerel
Bq
activity referred to a radionuclide
gray
Gy
absorbed dose
m^2*s^-2
J/Kg
sievert
Sv
equivalent dose
katal
kat
catalytic activity
mol*s^-1
Examples of coherent derived units in terms of base units
Derived quanity
Typical Symbol
square metre
m^2
area
cubic metre
m^3
volume
metre per second
m/s
speed, velocity
v
metre per second squared
m/s^2
acceleration
a
reciprocal metre
m^-1
wavenumber
vergence
V, 1/f
kilogram per cubic metre
kg/m^3
density
p
kilogram per square metre
kg/m^2
surface density
PA
cubic metre per kilogram
m^3/kg
specific volume
ampere per square metre
A/m^2
current density
ampere per metre
A/m
magnetic field strength
mole per cubic metre
mol/m^3
concentration
mass concentration
p, y
candela per square metre
cd/m^2
Lv
Examples of derived that include units with special names
pascal-second
Pa*s
dynamic viscosity
m^-1*kg*s^-1
newton-metre
N*m
moment of force
m^-2*kg*s^-2
newton per metre
N/m
surface tension
kg*s^-2
radian per second
rad/s
angular velocity, angular frequency
radian per second squared
rad/s^2
angular acceleration
s^-2
watt per square metre
W/m^2
heat flux density, irradiance
kg*s^-3
joule per kelvin
J/K
entropy, heat capacity
m^2*kg*s^-2*K^-1
joule per kilogram-kelvin
J/(kg*K)
specific heat capacity, specific entropy
m^2*s^-2*K^-1
joule per kilogram
J/kg
specific energy
watt per metre-kelvin
W/(m*K)
thermal conductivity
m*kg*s^-3*K^-1
joule per cubic metre
J/m^3
energy density
m^-1*kg*s^-2
volt per metre
V/m
electric field strength
m*kg*s^-3*A^-1
coulomb per cubic metre
C/m^3
electric charge density
m^-3*s*A
coulomb per square metre
C/m^2
surface charge density, electric flux density
m^-2*s*A
farad per metre
F/m
permittivity
m^-3*kg^-1*s^4*A^2
henry per metre
H/m
permeability
m*kg*s^-2*A^-2
joule per mole
J/mol
molar energy
m^2*kg*s^-2*mol^-1
joule per mole-kelvin
J/(mol*K)
molar entropy, molar heat capacity
m^2*kg*s^-2*K^-1mol^-1
coulomb per kilogram
C/kg
exposure (x, y-rays)
kg^-1*s*A
gray per second
Gy/s
absorbed dose rate
m^2*s^-3
watt per steradian
W/sr
radiant intensity
m^2*kg*s^-3
watt per square metre-steradian
W/(m^2*sr)
radiance
katal per cubic metre
kat/m^3
catalyic activity concentration
m^-3*s^-1*mol
SI prefixes
Prefix
Base
10
Decimal
quetta
Q
10^30
1000000000000000000000000000000
ronna
R
10^27
1000000000000000000000000000
yotta
Y
10^24
1000000000000000000000000
zetta
Z
10^21
1000000000000000000000
exa
E
10^18
1000000000000000000
peta
P
10^15
1000000000000000
tera
10^12
1000000000000
giga
G
10^9
1000000000
mega
M
10^6
1000000
kilo
10^3
1000
hecto
10^2
100
deca
da
10^1
(base)
10^0
deci
d
10^-1
0.1
centi
10^-2
0.01
milli
10^-3
0.001
micro
μ
10^-6
0.000001
nano
n
10^-9
0.000000001
pico
10^-12
0.000000000001
femto
f
10^-15
0.000000000000001
atto
10^-18
0.000000000000000001
zepto
z
10^-21
0.000000000000000000001
yocto
y
10^-24
0.000000000000000000000001
ronto
r
10^-27
0.000000000000000000000000001
q
10^-30
0.000000000000000000000000000001
Non-SI units accepted for use with SI units
Value in SI units
minute
min
1min = 60s
hour
1h = 60min = 3600s
day
1d = 24h = 1440min = 86400s
astronomical unit
au
1au = 149597870700m
plane and
phase angle
degree
arcminute
arcsecond
°
1 ° = pi/180 rad
'
1' = 1/60 ° = pi/10800 rad
"
1"= 1/60 ' = pi/648000 rad
hectare
ha
1ha = 1*hm^2 = 10^4*m^2
litre
l, L
1l = 1L = 1dm^3 = 10^3*cm^3 = 10^-3*m^3
tonne (metric ton)
t
1t = 1Mg = 10^3*kg
dalton
Da
1Da = 1.660539040*10^-27*kg
energy
electronvolt
eV
1eV = 1.602176634*10^-19*J
Logarithmic
ratio quantities
neper
Np
bel
B
decibel
dB
In using these units it is important that the nature of the quantity be specified
and that any reference value be specified
quecto
Unit name
Definition
The duration of 9192631770 periods of radiation
corresponding to the transition between two hyperfine
levels of ground state of the caesium-133 atom
The distance traveled by light in vacuum in
1/299792458 seconds
By setting the Planck constant h to 6.62607015*10^-34
J*s (J=kg*m^2*s^-2)
kg = h / 6.62607015*10^-34*m^2*s^-1
The flow of 1/1.602176634*10^-19 times
the elementary charge e per second
amount of substance of exactly 6.02214076*10^23
elementary entities (Avogadro Number)
light source that emits monochromatic radiation of frequency
5.4*10^14 Hz and has a radiant intensity in that direction
0f 1/683 watt per steradian
Table Of Equivalents
Inch
In
SI, SI derived Units
0.0245 m
foot
ft
0.3048 m
yard
yd
0.9144 m
mile
mi
1609.344 m
Acre
ac
4046.8564224 m^2
cubic Inch
In^3
0.016387064 L
cubic foot
ft^3
28.316846592 L
cubic yard
yd^3
cubic mile
mi^3
4168181797320.37776 L
gallon
gal
4.40488377086 L
barrel
bbl
158.987 L
square inch
In^2
0.00064516 m^2
Quart
qt
0.946352946 L
square foot
ft^2
0.09290304 m^2
pint
pt
0.473176473 L
square yard
yd^2
0.83612736 m^2
cup
0.2365882365 L
square mile
mi^2
2589988.110336 m^2
tablespoon
Tbsp
0.0148 L
teaspoon
tspn
0.005 L
fluid ounce
fl oz
0.02957353 L
ton
907.18474 kg
pound
lb
0.45359237 kg
ounce
0.02916 kg
oz
Fahrenheit
°F
K = (°F+459.67)*(5/9)
K = (°C+273.15)
bushel
bsh
35.2391 L
Angstrom
Å
10^-10*m
psi
lb/in^2
Pa/6894.757293168
atmosphere
atm
Pa/101325
Firewood Measurements
Cord
Compact Stack Of Firewood, 4 ft High x 8 ft Wide x 4 ft Deep
rick
Compact Stack Of Firewood, 4 ft High x 8 ft Wide x 12 in Deep
Volume
128 ft^3
32 ft^3
British Thermal Unit
Btu
(J/1055.1)/3600s
gram
g
kg/1000
