International System of Units

If people of every region use a different unit for weighing, the trade between these two regions will create problems. Now a days inter continental trade is common and the use of a common unit in measurement become essential.

SI (System International) presctibe the unit and it's symbol for international use.

Lenth, mass, time, temperature, volume etc are considered to be basic quantities. The standard unit for the measurement with it's symbol in bracket are

Length : metre (m)
Mass : gram (g)
Time : second (s)
Temperature : kelvin (K) also degree celcius (°C)
Volume : litre (l)

Units are always written singular. There is not dot after the unit symbol. One character space is provided between numeral and unit or it's symbol. Unit with the name of a scientist is always written in lowercase, while the symbol will be in Uppercase.

Eg :

Force : newton (N)
Energy : joule (J)
Power : watt (W)
Voltage : volt (V)
Current : ampere (A)

Prefixes permitted to use with standard symbols are

c - centi (10 ^-2)
m - milli (10 ^-3)
k - kilo (10 ^3)
M - mega (10 ^6)

Prefixes are helpful to write large and small measurements convienently.

Eg :

1,000 m = 1 km
1,000 ml = 1 l
11,000 V = 11 kV
1,000 mg = 1 g
1, 000 kg= 1 t (t, symbol for ton)