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International Starch Institute

Science Park Aarhus, Denmark

SI Units

| SI-units | UnitConversion | SteamTable | StarchViscosity | SieveComparison | TableIndex |

| Time | Mass | Length
| Temperature | Ampere | Mole
| Light | Radian | Steradian
| DerivedUnits | UnitPreFix |

**International System of
Base Units** (The seven base units):

The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.

The kilogram is defined as a mass equal to that of the International Prototype Kilogram - a platinum-iridium cylinder which in 1889 replaced the previous platinum protype matching the mass of 1 cubic decimetre of pure water at the temperature of its maximum density (4.0° C/39.2° F)).

The metre was 1960 redefined as 1,650,763.73 wavelengths of the reddish-orange light emitted by the isotope krypton-86. The metre was again redefined in 1983 as the length of the path travelled by light in a vacuum during a time interval of 1/299,792,458 of a second.

Since 1960 the temperature scale is based on the triple point of water. The triple point of a substance is the temperature and pressure at which its solid, liquid, and gas forms are in equilibrium. The temperature of 273.16 K (kelvins) was assigned to this point. The freezing point of water was designated as 273.15 K, equalling exactly 0° on the Celsius temperature scale. The Celsius scale has been redefined in terms of Kelvin temperatures, so that now absolute zero, 0 K, is at -273.15° C. As a consequence the freezing and boiling points of water are at present determined as 0° C and 99.974° C respectively.

The ampere was defined as the constant electric current that, flowing in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one metre apart in a vacuum, would produce between these conductors a force equal to 2 × 10-7 newton per metre of length.

In 1971 the
mole was defined as the amount of substance of a system that contains as many elementary
entities—which may be molecules, atoms, ions, and so on—as there are atoms in
0.012 kilogram of carbon-12. This number, known as Avogadro’s Number, is about 6.022
× 10^{23}.

In 1979 the
candela was redefined as the luminous intensity, in a given direction, of a source that
emits monochromatic radiation of frequency 540 × 10^{12} hertz (cycles per second) and that has a radiant intensity of (1/638) watt per
steradian.

**International System of ****Supplementary Units** (Two supplementary
units):

The radian is the plane angle between two radii of a circle that cut off on the circumference an arc equal in length to the radius.

The steradian is the solid angle that, having its vertex at the centre of a sphere, cuts off an area of the surface of the sphere equal to that of a square with sides of length equal to the radius of the sphere. The radian and the steradian are classed as derived units.

**Derived Units** (Nine common units derived from SI base
units)

Area square |
meter |
m2 |

Volume |
cubic meter |
m3 |

Velocity |
meter per second |
m/s |

Acceleration |
meter per second squared |
m/s2 |

Density |
kilogram per cubic meter |
kg/m3 |

Current density |
ampere per square meter |
A/m2 |

Magnetic field strength |
ampere per meter |
A/m |

Specific volume |
cubic meter per kilogram |
m3/kg |

Luminance |
candela per square meter |
cd/m2 |

**Derived Units
assigned special names** (Units derived from SI base and supplementary units)**:**

Frequency |
hertz |
Hz |
1/s |

Force |
newton |
N |
kg·m/s2 |

Pressure/stress |
pascal |
Pa |
N/m2 |

Energy/work/quantity of heat |
joule |
J |
N·m |

Power |
watt |
W |
J/s |

Quantity of electricity |
coulomb |
C |
A·s |

Electric potential |
volt |
V |
W/A |

Capacitance |
farad |
F |
G/V |

Electric resistance |
ohm |
W |
V/A |

Conductance |
siemens |
S |
A/V |

Magnetic flux |
weber |
Wb |
V·s |

Magnetic flux density |
tesla |
T |
Wb/m2 |

Inductance |
henry |
H |
Wb/A |

Luminous flux |
lumen |
lm |
cd·sr |

Illuminance |
lux |
lx |
lm/m2 |

Activity of radionuclides |
becquerel |
Bq |
1/s |

Absorbed dose |
gray |
Gy |
J/kg |

Dose equivalent |
sievert |
Sv |
J/kg |

Factor |
Name |
Symbol |

10^{24} |
yotta | Y |

10^{21} |
zetta | Z |

10^{18} |
exa | E |

10^{15} |
peta | P |

10^{12} |
tera | T |

10^{9} |
giga | G |

10^{6} |
mega | M |

10^{3} |
kilo | k |

10^{2} |
hecto | h |

10 | deca | da |

10^{-1} |
deci | d |

10^{-2} |
centi | c |

10^{-3} |
milli | m |

10^{-6} |
micro | µ |

10^{-9} |
nano | n |

10^{-12} |
pico | p |

10^{-15} |
femto | f |

10^{-18} |
atto | a |

10^{-21} |
zepto | z |

10^{-24} |
yocto | y |

| Top of Page | SI-units |UnitConversion | SteamTable | StarchViscosity | SieveComparison | TableIndex |

| Time | Mass | Length
| Temperature | Ampere | Mole
| Light | Radian | Steradian
| DerivedUnits | UnitPreFix |

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Keywords: conversion metric SI imperial unit temperature pressure volume length heat energy mass area