Introduction to SI Units List

Physical quantities were measured in terms of standardized values called units. 

For Example - In this picture below, 

       length of a road- a physical quantity

       Expressed in kilometers or meters- km/m are units.

If units are not clearly mentioned, then it could be difficult to compare the measured values elaborately.  

(Image to be added soon)

Units are measured in two ways- SI units (metric system) and English units (imperial system) 

English system is widely used in the US. In the present times, every country has accepted SI units as standardized units, so mathematicians and scientists are accepting SI units as the universal method. 

The International System of Units (SI) is defined as a metric system that is used as a measurement standard accepted globally. SI unit is derived from the French word Systeme International. It plays a vital role in developing scientific and technical research to avoid confusion within units. It consists of 7 base units that define 22 derived units. The quantities are defined with the power of 10, ranging from 10-24 to 1024. It is expressed as fractional or standard quantities. 


Listed Below is The Table Which Represents SI Units

Sl. No.

Quantity Name

SI Unit

SI Unit System

1

Length (L)

Meter

M

2

Time (T)

Second

S

3

Mass (M)

Kilogram

Kg

4

Electric Current (I)

Ampere

A

5

Amount Of Substance (N)

Mole

Mol

6

Thermodynamics Temperature (Θ)

Mole

K

7

Luminous Intensity (J)

Candela

cd


List of SI Units

SI units are used in physics to express different quantities which are classified to: 

Basic units and Derived units.

  1. SI Basic Units

Basic units are known as the fundamental units which are mostly used as the building block of the system of units and then the other units can be derived from SI basic units. 

List of SI Basic units

There are 7 SI basic units. These units are interdependent with each other mutually stating Base Units.  Each unit along with its SI units, symbol, and expressions are given below:

Unit of Measurement

SI Unit

Description

Unit of length.

Meter (m).

It is defined by considering a fixed value of the speed of the light in a vacuum. This is expressed as m.s-1.


Unit of time

Second (s)

It is defined as the constant value of cesium frequency and is expressed as s. 


Unit of the mass

Kilogram (kg)

It is defined by considering the constant value of plank. It is expressed as kg.m2.s-1


Unit of electric current

Ampere (A)

It is defined by considering the constant value of the elementary charge. 


Unit of luminous intensity

Candela (cd)

The luminous intensity is defined by the constant value of luminous efficacy.

Unit of the amount of substance

Mole (mol)

It is defined by the constant value of Avogadro constant (NA) fair one mole is 6.02214076 × 1023 elementary entities. It is expressed as mol-1


Unit of thermodynamics temperature

Kelvin (k)

Thermodynamics temperature is defined by taking the constant value of Boltzmann constant where k = 1.38 0649 ×10-23



  1. SI Derived Units:

There are only limited derived units that form different operations over the base units. In the case of derived units, the dimensions are expressed related to the dimensions of the base units. It can also be expressed by combining base and derived units.

List of SI Derived Units

Sl no

Unit names

SI Unit

Symbols of SI Units

Expressions in SI Base unit

Other SI Units

1

Force Or Weight

Newton

N

kg.g.s-2

-

2

Electric Charge

Coulomb

C

s.A

-

3

Frequency

Hertz

Hz

s-1

-

4

Electric Potential

Volt

V

kg.m2.s-3.A-1

W/A

5

Capacitance

Farad

F

kg.m2.s-2.A-2

Wb/A

6

Inductance

Henry

H

kg−1.m−2.s4.A2

C/V

7

Resistance, Impedance, Reactance

Ohm 

kg−1.m−2.s4.A2

V/A

8

Electric Conductance

Siemens

S

kg−1.m−2.s3.A2

Ω-1

9

Magnetic Flux

Weber

Wb

kg.m2.s−2.A−1

V.s

10

Magnetic Flux Density

Tesla

T

kg.s−2.A−1

Wb/m2

11

Energy, Work, Heat

Joule

J

kg.m2.s−2

N.m

12

Power, Radiant Flux

Watt

W

kg.m2.s−3

J/s

13

Angle

Radian

Rad

m.m-1

-

14

Radio Activity

Becquerel

Bq

s-1

-

15

Luminous Flux

Lumen

Im

cd

cd.sr


These SI units are mostly used units. Other than these there are certain units feature mostly seen in physics such as

  • SI unit of velocity is meter per second (m/s)

  • SI unit of heat is the unit joule.

  • SI unit of momentum is kilogram meter per second (kg.m/s)

  • The SI unit of the magnetic field is Tesla.

There are numerous numbers, terms and quantities studied in physics which are expressed in various units. One must know the CGS and the SI units frequently to ace in physics. 


Advantages of CGS Units and SI Units

  • SI units and CGS units questions are very common in physics examinations

  • The units and explanations can help to get into the depth of different topics.

  • These are provided in an interactive manner to understand easily.

  • These units are provided in points so that the concept will remain clear for a longer time.


Units of Measurement for Length, Time, Mass And Volume

  1. Length

The SI unit of length is a meter. It is defined as the length traveled by night in a path is 1/299792458 seconds. 

(Image to be added soon)

Some other units of length include nanometres, millimeters, decimeters, centimeters, meters, kilometers.

Non-SI units of length include yard, inch, foot.


  1. Time 

The SI unit of time is second. It can be considered as the time-taken, which is equal to 9192631770 vibrations of radiation to the distance between two hyperfine intervals of the cesium-133 atom. Time is a continuous process of existence to the future, present, and past. To know about the existence of any being, units of time are considered. The units of time are an hour, minute, and second. 

Units of time are

Minute = 60 seconds

Hour = 60 minutes

Day = 24 hours

Week = 7 days

Month = 28 to 31 days

Year = 365 /366 days


  1. Mass

One thing you must keep in mind is that mass is different from weight. Mass is defined as the quantity of matter in an object. The most used units for the measurement of mass are gram and kilogram.

SI unit of mass is the kilogram (kg)

Other units of mass are 

Milligram = 1/1000g

Decigram = 1/10g

Centigram = 1/100g

Gram = 1000 milligrams

Decagram= 10 grams

Hectogram = 100 grams

Metric ton =1000 kilograms

Kilogram = 1000 grams


  1. Volume 

Capacity is measured by volume. To measure the capacity of an object the unit of volume is required. The SI unit of volume is measured in cubic meters. 

1m3= 1m ×1m ×1m

Some Other Units Of Volume Are

Unit of Measure

Cubic Meter

1 cubic metre 

1

1 barrel

0.1589

1 cubic foot

0.02 83

1 cubic decimeter

0.001

1 litre

0.001

1 gallon

0.0037 8

1 pint

0.0004 73

1 cubic inch

0.00001 6

1 cubic centimetre

0.000001

FAQs (Frequently Asked Questions)

1. How do you differentiate the SI unit names and symbols?

SI unit names and symbols are very original words and letters that are in a very constant form. Let us illustrate some examples.


Unit Names

Unit Symbols

Unit names are written in the form of capital letters if it's the name of the inventor or their titles. For example- Watt is named after the inventor James Watt. So, while writing we write megawatt not megaWatt.              

Symbols are case sensitive so we write MW for megawatt and mW for milliwatt.



While writing units it is singular and plural as well.  For example- one meter, five meters. But five hertz as the plural form of hertz is hertz, joule is joule, etc.      

Unit symbols have no plurals forms. We must write for 1m, 5m, etc.



Unit names are pronounced and written in different languages differently. For example, in the US it is written as “metre”, in French it's “metre”, in German it's “meter”, and in Spanish, it's “metro”.      

Unit symbols are the same in different languages. Absolutely no changes in it. It's “m” for meters globally.


2. Why are SI units called a coherent system of units?

In the coherent unit system, we choose several base units for a set of fundamental quantities and derive other units by dividing or multiplying any constant into it resulting in the same form of numerical and physical units.

So the term SI units are the total set of base units, derived units with decimal multiples and submultiples. 

For example, kilometres, meter, and millimetres are SI units, likewise meter per second and millimetre per second. From that group, “meter” and “meter per second” are termed as coherent SI units.