Sub Topics

Unit conversion is a process of converting the unit of a physical quantity from one unit to another. Some basic conversion rules are there of every quantity. According to our requirements one can change the unit by using the basic rules. Some of the conversion rules which we are dealing frequently are given in this section.

The metric system is the system of measurement used by most countries in the world. All countries, including the United States, use it for scientific purposes. The metric system, like our decimal numeration system, is based on the number 10. For this reason, converting from one metric unit to another is easier than with the American system.
For each type of physical quantity, a main table is provided, in which the conversion factors are given in scaled form, consisting of a 5 digit number, followed by the power of 10 by which it is to be multiplied. For instance, to convert kilocalories per day into watts, the entry in the "power table" is 4.8458; 2. This means, multiply by 4.8458$\times10^{2}$ in other words, by 0.048458. In most cases, the conversion factor from any unit to any other can be found by looking up a single entry in the main table, but in some cases the conversion factors between different metric units have been relegated to supplementary tables.Some conversions have to be done in two stages.
SI units of some important physical quantity which we are used commonly is given as follows. Derived quantity 
Symbol 
Unit 
Area  A  m^{2} 
Volume  V  m^{3} 
Density  ρ  kgm^{3} 
Velocity  v  ms^{1} 
Acceleration  a  ms^{2} 
Momentum  p  kgms^{1} 
Force  F  N 
Pressure  p  Pa 
Energy  E  J 
Heat  Q  J 
Power  P  W 
Frequency  f  Hz 
Resistance  R  Ω 
Capacitance  C  F 
Inductance  L  H 
Various units of length and its conversions are given below.
1 centimeter = 10 millimeter
1 decimeter = 10 centimeter
1 meter = 10 decimeter
1 dekameter = 10 meter
1 kilometer = 1000 meter
1 angstrom = 10^{10} meter
1 inch = 25.4 millimeter
1 feet = 12 inches Area unit conversion from different units to meter square is given as follows:
1 acre = 4.0468$\times10^{3}$ meter square
1 square foot = 9.2903$\times10^{2}$ meter square
1 hectare = $10^{4}$ meter square
1 square inch = 6.4516$\times 10^{4}$ meter square
1 barn = $10^{28}$ meter square
1 square mile = 2.5888$\times10^{6}$ meter square Commonly used mass unit conversions are given below:
1 gram = 0.001 kilograms
1 milligrams = 0.000001 kilograms
1 pounds = 0.453592 kilograms
1 grains = 0.000065 kilograms
1 hectograms = 0.1 kilograms
1 quintal = 100 kilograms
1 tonnes = 1000 kilograms Volume unit conversion is listed below:
1 cubic meters = 1000 liters
1 cubic centimeters = 0.001 liters
1 cubic inches = 0.016387 liters
1 centiliters = 0.01 liters
1 microliters = 0.000001 liters
1 table spoon = 0.014787 liters
1 barrels = 158.987295 liters
Different unit conversion of time is listed here.
1 minutes = 60 seconds
1 hours = 3600 seconds
1 days = 86400 seconds
1 weeks = 604800 seconds
1 milliseconds = 0.001 seconds
1 microseconds = 0.000001 seconds Unit conversions of force are,
1 dynes = 0.00001 newtons
1 kilograms force = 9.80665 newtons
1 pounds force = 4.448222 newtons
1 tonnes force = 9806.65 newtons
1 tons force = 9964.016418 newtons Important unit conversions related to energy are,
1 ergs = $10^{7}$ joules
1 watt hours = 3600 joules
1 calories = 4.186 joules
1 kilojoules = 1000 joules
1 electron volts = 1.6$\times10^{19}$ joules
Some conversions of power units are given in this section.
1 horse power = 746 watts
1 joules/hour = 0.000278 watts
1 kilowatts = 1000 watts
1 megawatts = $10^{6}$ watts
1 terawatts = $10^{12}$ watts
1 petawatts = $10^{15}$ watts Generally used unit conversions of density are listed here.
1 kilograms/liter = 1000 kilogram/cubic meter
1 ounces/cubic inch = 1729.9940 kilogram/cubic meter
1 pounds/cubic inch = 27679.904 kilogram/cubic meter
1 grams/cubic centimeters = 1000 kilogram/cubic meter
1 slugs/cubic foot = 515.317882 kilogram/cubic meter Important viscosity unit conversions are,
1 poise = 0.1 kilogram/meter second
1 millipascal second = 0.001 kilogram/meter second
1 pound/foot second = 1.48816 kilogram/meter second
1 pascal second = 1 kilogram/meter second Let us discuss some unit conversion problems.
Solved Examples
Question 1: Convert the given unit of distance in to meters; 5 km and 25 inch?
Solution:
We know that,
1 km = 1000 m
So, 5 km = 5$\times$1000 = 5000 m
1 inch = 0.0254 m
So, 25 inches = 25$\times$0.0254 = 0.635m
Solution:
We know that,
1 km = 1000 m
So, 5 km = 5$\times$1000 = 5000 m
1 inch = 0.0254 m
So, 25 inches = 25$\times$0.0254 = 0.635m
Question 2: Convert the given unit of mass into kg; 15 pounds and 10 hectograms?
Solution:
We know that,
1 pounds = 0.453592 kg
So, 15 pounds = 15$\times$0.453592 = 6.803 kg
1 hectograms = 0.1 kg
So, 10 hectograms = 0.1$\times$10 = 1 kg
Solution:
We know that,
1 pounds = 0.453592 kg
So, 15 pounds = 15$\times$0.453592 = 6.803 kg
1 hectograms = 0.1 kg
So, 10 hectograms = 0.1$\times$10 = 1 kg