Watch Free Classes

Do you know what units are?

Well, Units are those physical quantities which are used for measuring anything or we can say it tells us about the amount of any substance. Like, Metre is the unit for measuring length, kilogram measures weight, cubic metre tells us the amount of volume.

We have different units, and can convert them into each other.

You will be provided with tables which help you in conversion, before proceeding, it is necessary to know different systems of units.

System of Units

In the system of units, some quantities are fundamental, while others can be derived from them. Mostly, “Length, Mass and time” are considered as fundamental quantities while others can be derived from them.

Commonly, Four system of units are used as following:-

  • MKS : M – metre, K – Kilogram, S – Second

metre is for measuring length, K is for kilogram and S is for measuring Time.

  • CGS : C – Centimetre, G – Gram, S – Second

Centimetre is for measuring length, G is for measuring Weight and S – Second is the unit of time.

  • FPS – F – Feet (Unit of length), P – Pound ( Unit Of Weight) and S – Second (Unit of Time).
  • SI Unit – SI is the international system of units, This system has 7 fundamental quantities and others can be derived from them.

S. No.

Name of the Quantity

SI Unit

SI Unit Symbol

1.

Length (l)

metre

m

2.

Mass (M)

Kilogram

kg

3.

Time (T)

Second

s

4.

Electric current (I)

Ampere

A

5.

Thermodynamic temperature (Θ)

Kelvin

K

6.

Amount of substance (N)

Mole

mol

7.

Luminous intensity (J)

Candela

cd

So, these are the four common systems of units, and now we are going to discuss their conversion, by using a conversion table.

Length Unit Conversion

1 millimetre

10-3 metre

1 centimetre

10-2 metre

1 decimetre

10-1 metre

1 decametre

10 metres

1 hectometre

102 metres

1 kilometre

103 metres

1 inch

2.54 × 10-2 metres

1 foot

0.3048 metres

1 Angstrom

10-10 metres

1 Fermi

10-15 metres

1 light year

0.946 × 1016 metres

1 mile

1.609344 km

Volume Unit Conversion

1 millilitre

10-3 litre

1 centilitre

10-2 litre

1 decilitre

10-1 litre

1 decalitre

10 litres

1 hectolitre

102 litres

1 kilolitre

103 litres

1 cubic inch

1.639 × 10-2 litres

1 gallon

3.785 litres

1 cubic foot

28.316 litres

Mass Conversion

1 milligram

10-3 gram

1 centigram

10-2 gram

1 decigram

10-1 gram

1 decagram

10 gram

1 hectogram

102 gram

1 kilogram

103 grams

1 stone

6350.29 grams

1 pound

453.592 grams

1 ounce

28.3495 grams

Time Unit Conversion

1 minute

60 seconds

1 hour

60 minutes / 3600 seconds

1 day

24 hours

1 week

7 days

1 year

365 days

Area Unit Conversion

1 sq. inch

6.4516 x 10-4 square metre

1 sq. foot

9.2903 x 10-2 square metre

1 acre

4.0468 x 103 square metre

1 hectare

1 x 104 square metre

1 sq. mile

2.5888 x 106 square metre

1 barn

1 x 10-28 square metre

Force Unit Conversion

1 dyne

1 x 10-5 Newton

1 pound

4.448 Newton

Power Unit Conversion

1 erg/sec

1 x 10-5 watt

1 BTU/hr

0.2930 watt

1 foot-pound/ sec

1.356 watt

1 horsepower

745.7 watt

1 calorie/sec

4.186 watt

Energy Unit Conversion

1 BTU (British thermal unit)

1055 Joule

1 erg

1×10-7 Joule

1 foot-pound

1.356 Joule

1 calorie

4.186 Joule

1 kilowatt-hour

3.6×106 Joule

1 electron volt

1.602×10-19 Joule

1 litre atmosphere

101.13 Joule

So, these are the tables which will help us in converting them into each other. Some examples are given below, which will make your understanding clear and better.

Examples

1. A box weighs 5 pounds, convert this weight into kilograms.

Ans: m = 5 pounds

We know that, 

1 pound = 453.592 grams

⇒5 pound=5× 453.592 grams

=2267.96 grams

As we know,

1000 grams  = 1 kilogram

⇒1 gram=10-3 kilogram

2267.96 grams = 10-3 × 2267.96 kilogram

= 2.267 kilograms

2. Distance between two cities is 6000 cm, calculate it in kilometres.

Ans: 1 km = 1000 m

1 m = 100 cm

1 cm = 10-2 m

      6000 cm = 6000 × 10-2 m

= 60 m

      60 m = 60 × 10-3 km

                = 0.06 km

Conclusion

We have studied unit conversion. As it is a very important part of our daily life. It is important also, as Different countries have different units for measuring physical quantities. So it becomes difficult to understand this for us. That’s why we should have knowledge of unit conversion.