Browse Definitions:
Definition

# International System of Units (SI)

The International System of Units (abbreviated SI from systeme internationale , the French version of the name) is a scientific method of expressing the magnitudes or quantities of important natural phenomena. There are seven base units in the system, from which other units are derived. This system was formerly called the meter-kilogram-second (MKS) system.

All SI units can be expressed in terms of standard multiple or fractional quantities, as well as directly. Multiple and fractional SI units are defined by prefix multipliers according to powers of 10 ranging from 10 -24 to 10 24 .

SI base units:
The meter (abbreviation, m) is the SI unit of displacement or length. One meter is the distance traveled by a ray of electromagnetic (EM) energy through a vacuum in 1/299,792,458 (3.33564095 x 10 -9 ) second. The meter was originally defined as one ten-millionth (0.0000001 or 10 -7 ) of the distance, as measured over the earth's surface in a great circle passing through Paris, France, from the geographic north pole to the equator.

The kilogram (abbreviation, kg) is the SI unit of mass. It is defined as the mass of a particular international prototype made of platinum-iridium and kept at the International Bureau of Weights and Measures. It was originally defined as the mass of one liter (10 -3 cubic meter) of pure water.

The second (abbreviation, s or sec) is the SI unit of time. One second is the time that elapses during 9.192631770 x 10 9 cycles of the radiation produced by the transition between two levels of Cesium 133. It is also the time required for an EM field to propagate 299,792,458 (2.99792458 x 10 8 ) meters through a vacuum.

The kelvin (abbreviation K), also called the degree Kelvin (abbreviation, o K), is the SI unit of temperature. One Kelvin is 1/273.16 (3.6609 x 10 -3 ) of the thermodynamic temperature of the triple point of pure water (H 2 O).

The ampere (abbreviation, A) is the SI unit of electric current. One ampere is the current that would produce a force of 0.0000002 (2 x 10 -7 ) newton between two straight, parallel, perfectly conducting wires having infinite length and zero diameter, separated by one meter in a vacuum. One ampere represents 6.24 x 10 18 unit electric charge carriers, such as electrons, passing a specified fixed point in one second.

The candela (abbreviation, cd) is the SI unit of luminous intensity. It is the electromagnetic radiation, in a specified direction, that has an intensity of 1/683 (1.46 x 10 -3 ) watt per steradian at a frequency of 540 terahertz (5.40 x 10 14 hertz).

The mole (abbreviation, mol) is the SI unit of material quantity. One mole is the number of atoms in 0.012 kilogram of the most common isotope of elemental carbon (C-12). This is approximately 6.022169 x 10 23 , and is also called the Avogadro constant.

SI derived units include the hertz , the newton , the pascal (unit of pressure or stress) , the ohm , the farad , the joule , the coulomb , the tesla , the lumen , the becquerel , the siemen , the volt , and the watt .

These units are included in our Table of Physical Units .

This was last updated in March 2011

#### Join the conversation

Send me notifications when other members comment.
It is a very website.
Cancel
worldwide SI system acceptence date
Cancel
informative
Cancel
The units of absolute temperature are kelvins, with a small 'k'. They are not degrees. To say degrees Kelvin is wrong.
Cancel
no useful information
Cancel
useful information but can't be trusted
Cancel
imlike
Cancel
��������������������
Cancel

## SearchCompliance

• ### PCAOB (Public Company Accounting Oversight Board)

The Public Company Accounting Oversight Board (PCAOB) is a Congressionally-established nonprofit that assesses audits of public ...

• ### cyborg anthropologist

A cyborg anthropologist is an individual who studies the interaction between humans and technology, observing how technology can ...

• ### RegTech

RegTech, or regulatory technology, is a term used to describe technology that is used to help streamline the process of ...

## SearchSecurity

• ### email spam

Email spam, or junk email, is unsolicited bulk messages sent through email with commercial, fraudulent or malicious intent.

• ### distributed denial of service (DDoS) attack

A distributed denial-of-service attack occurs when an attack originates from multiple computers or devices, usually from multiple...

• ### application whitelisting

Application whitelisting is the practice of identifying applications that have been deemed safe for execution and restricting all...

## SearchHealthIT

• ### athenahealth Inc.

Based in Watertown, Mass., athenahealth Inc. is a leading vendor of cloud-based EHRs for small to medium-sized physician ...

• ### Affordable Care Act (ACA or Obamacare)

The Affordable Care Act (ACA) is legislation passed in 2010 that changed how uninsured Americans enroll in and receive healthcare...

• ### HIPAA Privacy Rule

The Standards for Privacy of Individually Identifiable Health Information, commonly known as the HIPAA Privacy Rule, establishes ...

## SearchDisasterRecovery

• ### disaster recovery as a service (DRaaS)

One approach to a strong disaster recovery plan is DRaaS, where companies offload data replication and restoration ...

• ### data recovery

Data recovery restores data that has been lost, accidentally deleted, corrupted or made inaccessible. Learn how data recovery ...

• ### disaster recovery plan (DRP)

A company's disaster recovery policy is enhanced with a documented DR plan that formulates strategies, and outlines preparation ...

## SearchStorage

• ### virtual memory

Virtual memory is a memory management capability of an OS that allows a computer to compensate for physical memory shortages by ...

• ### yottabyte (YB)

A yottabyte is a measure of theoretical storage capacity and is 2 to the 80th power bytes, or, in decimal, approximately 1,000 ...

• ### Kilo, mega, giga, tera, peta, exa, zetta and all that

Kilo, mega, giga, tera, peta, exa, zetta are among the list of prefixes used to denote the quantity of something, such as a byte ...

## SearchSolidStateStorage

• ### PCIe SSD (PCIe solid-state drive)

A PCIe SSD (PCIe solid-state drive) is a high-speed expansion card that attaches a computer to its peripherals.

• ### SSD caching

SSD caching, also known as flash caching, is the temporary storage of data on NAND flash memory chips in a solid-state drive so ...

• ### NVDIMM (Non-Volatile Dual In-line Memory Module)

An NVDIMM (non-volatile dual in-line memory module) is hybrid computer memory that retains data during a service outage.

## SearchCloudStorage

• ### RESTful API

A RESTful application program interface breaks down a transaction to create a series of small modules, each of which addresses an...

• ### cloud storage infrastructure

Cloud storage infrastructure is the hardware and software framework that supports the computing requirements of a private or ...

• ### Zadara VPSA and ZIOS

Zadara Storage provides block, file or object storage with varying levels of compute and capacity through its ZIOS and VPSA ...

Close