SI units

In Europe and the UK, the units for measuring different properties
are known as SI units. SI stands for Système Internationale.
All units are derived from seven base units.
Base quantity Base unit Symbol
Time Second s
Electrical current Ampere A
Length Metre m
Mass Kilogram kg
Temperature Kelvin K
Luminous intensity Candela cd
Amount of substance Mole mol

SI-derived units Derived quantity Name Symbol

Frequency Hertz Hz
Force Newton N
Energy, work, quantity of heat Joule J
Electric charge, quantity of electricity Coulomb C
Power Watt W
Potential difference,electromotive force Volt V or U
Capacitance Farad F
Electrical resistance Ohm Ω
Magnetic flux Weber Wb
Magnetic flux density Tesla T
Inductance Henry H

Luminous flux Lumen cd
Area Square metre m²
Volume Cubic metre m³
Velocity, speed Metre per second m/s
Mass density Kilogram per cubic metre kg/m3
Luminance Candela per square metre cd/m²

SI unit prefixes

Name Multiplier Prefix Power of 10
Tera 1000 000 000 000 T 1×1012
Giga 1000 000 000 G 1×109
Mega 1000 000 M 1×106
Kilo 1000 k 1×103
Unit 1
Milli 0.001 m 1×10−3
Micro 0.000 001 m 1×10−6
Nano 0.000 000 001 n 1×10−9
Pico 0.000 000 000 001 ρ 1×10−12
Examples
mA Milliamp = one thousandth of an ampere
km Kilometre = one thousand metres
μv Microvolt = one millionth of a volt
GW Gigawatt = one thousand million watts
kW Kilowatt = one thousand watts