# International System of Units (SI)

SI Units are the formal terms, definitions, and symbols used in the metric system. SI units start from base units which are the axiomatic building blocks from which all other units, called derived units, are created.

Base units include standard measures for time (second), distance (meter), mass (kilogram), pressure (bar), and more. Derived units combine base units, for example velocity ($v$) is distance ($d$) over time ($t$), or $v=d/t$.

## SI Unit Prefixes

PrefixSymbolValue
tera$T$$10^{12}$
giga$G$$10^{9}$
mega$M$$10^{6}$
kilo$k$$10^{3}$
hecto$h$$10^{2}$
deca$h$$10^{1}$
deci$d$$10^{-1}$
centi$d$$10^{-2}$
milli$m$$10^{-3}$
micro$μ$$10^{-6}$
nano$n$$10^{-9}$

## Deeper Knowledge on International System of Units (SI) ### Conductance and Siemens

The ability to conduct to current, measured in siemens ### Bureau International des Poids et Mesures (BIPM)

Keepers of SI Units and UTC time scale ### Charge and Coulombs

How force is exerted in electromagnetic field, measured in coulombs ### Resistance and Ohms

Opposition to current, measured in ohms ### Frequency and Hertz (Hz)

The number of times something happens per second ### Scientific Notation

Expressions of very large and very small numbers in science and math ### Engineering Notation

Expressions of very large and very small numbers for engineers ### Current and Amperes

The flow of electricity, measured in amps ### Voltage and Volts

Electrical potential energy, measured in volts ### Watt's Law (Power Law)

A formula to define the relationship between power, voltage, and current (P=IV)

## Broader Topics Related to International System of Units (SI) ### Science

The most rigorous system of epistemology ### Engineering

Apply science to create technology