Mathematical quantities such as length, volume, mass etc. are expressed in certain standards of measurement. These measurement standards are known as units. - SI (International System of Units, Meter, Kilogram, Second) system
- CGS
(Centimeter Gram Second) system
- FPS (Foot Pound Second) system
This process is called conversion of units. One unit can be converted into another unit by the use of conversion factor. This conversion factor is a constant value. When we multiply or divide the conversion factor with a unit, then it will be converted into another unit. Unit conversion is possible only for the same quantity. In other words, a unit of length can be converted only into another unit of length. |

- $1\ kilometer=1000\ meter$ or $1\ km=1000\ m$
- $1\ hectometer=100\ meter$ or $1\ hm=100\ m$
- $1\ decameter=10\ meter$ or $1\ dam=10\ m$
- $1\ decimeter$ = $\frac{1}{10}$$\ meter$ or $1\ dm$ = $\frac{1}{10}$$\ meter$
- $1\ centimeter$ = $\frac{1}{100}$$\ meter$ or $1\ cm$ = $\frac{1}{100}$$\ m$
- $1\ millimeter$ = $\frac{1}{1000}$$\ meter$ or $1\ mm$ = $\frac{1}{1000}$$\ m$
- $1\ cm=0.394\ inch$
- $1\ foot=12\ inch$
- $1\ inch=2.54\ cm$
- $1\ foot=0.3048\ m$
- $1\ yard=0.9144\ m$
- $1\ mile=1.61\ km$
- $1\ angstrom=10^{-10}\ meter$

^{2}. It can be converted into other units. The list of area unit conversion factors is given below:

- $1\ km^{2}=10^{6}\ m^{2}$
- $1\ hm^{2}=10^{4}\ m^{2}$
- $1\ dam^{2}=10^{2}\ m^{2}$
- $1\ dm^{2}=10^{-2}\ m^{2}$
- $1\ cm^{2}=10^{-4}\ m^{2}$
- $1\ mm^{2}=10^{-6}\ m^{2}$
- $1\ hectare=10^{4}\ m^{2}$
- $1\ square foot=0.092903\ m^{2}$

^{3}. Volume is expressed as liter also. Volume units can be converted into other units. The list of volume unit conversion factors is given below:

- $1\ kiloliter=1000\ liter$ or $1\ kl=1000\ l$
- $1\ hectoliter=100\ liter$ or $1\ hl=100\ l$
- $1\ decaliter=10\ liter$ or $1\ dal=10\ l$
- $1\ deciliter$ = $\frac{1}{1000}$$\ liter$ or $1\ dl$ = $\frac{1}{10}$$\ l$
- $1\ centiliter$ = $\frac{1}{100}$$\ liter$ or $1\ cl$ = $\frac{1}{100}$$\ l$
- $1\ milliliter$ = $\frac{1}{1000}$$\ liter$ or $1\ ml$ = $\frac{1}{1000}$$\ l$
- $1\ gallon=3.78541\ liter$
- $1\ liter=1000\ cubic\ centimeter$

- $1\ kilogram=1000\ gram$ or $1\ kg=1000\ g$
- $1\ hectogram=100\ gram$ or $1\ hg=1000\ g$
- $1\ decagram=10\ gram$ or $1\ dag=10\ g$
- $1\ decigram$ = $\frac{1}{1000}$$\ gram$ or $1\ dg$ = $\frac{1}{10}$$\ g$
- $1\ centigram$ = $\frac{1}{100}$$\ gram$ or $1\ cg$ = $\frac{1}{100}$$\ g$
- $1\ milligram$ = $\frac{1}{1000}$$\ gram$ or $1\ mg$ = $\frac{1}{1000}$$\ g$
- $1\ pound=453.592\ gram$
- $1\ ounce=28.3495\ gram$
- $1\ stone=6350.29\ gram$

^{}. The list of time unit conversion factors is given below:

- $1\ hour = 60\ minutes = 3600\ seconds$
- $1\ minute = 60\ seconds$
- $1\ millisecond = 10^{-3}\ seconds$
- $1\ microsecond = 10^{-6}\ seconds$
- $1\ nanosecond = 10^{-9}\ seconds$