International Starch Institute: SI units

Home	Profile	Market Place	Sweeteners	Lab Methods	Glossary	Search
Master Index	Environment	Application	Starch	Statistics	Tables	Write us

International Starch Institute
Science Park Aarhus, Denmark
SI Units

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

Time

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.

Mass

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)).

Length

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.

Temperature

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.

Ampere

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.

Mole

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 × 10²³.

Light

In 1979 the candela was redefined as the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 10¹² hertz (cycles per second) and that has a radiant intensity of (1/638) watt per steradian.

International System of Supplementary Units (Two supplementary units):

Radian

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.

Steradian

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

Prefix

Factor	Name	Symbol
10²⁴	yotta	Y
10²¹	zetta	Z
10¹⁸	exa	E
10¹⁵	peta	P
10¹²	tera	T
10⁹	giga	G
10⁶	mega	M
10³	kilo	k
10²	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

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