# 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

Prefix | Symbol | Value |
---|---|---|

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 | $n$ | $10^{-9}$ |

## SI Resources

## 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