Units in LaTeX

Note

TLDR: It is recommended to use the siunitx package for typesetting units in LaTeX. The units package is simpler and easier to use, but it is also less powerful and flexible.

There are a few ways to typeset units in LaTeX. The two most common ways are to use the siunitx package or to use the units package. The siunitx package is more powerful and flexible, but the units package is simpler and easier to use. This document will cover both methods.

siunitx

The siunitx provides a wide range of options for formatting units, including the ability to control the spacing between the number and the unit, the ability to automatically convert units, and the ability to define custom units.

Basic Usage

To use the siunitx package, you must first include it in your document preamble:

\usepackage{siunitx}

Note

Since version 3 it is no longer recommended to use \si or \SI anymore as they are deprecated. Instead, use \qty, \unit, etc.

Numbers can be typeset with \num:

\num{3.14159e-21}

This will produce the output \(3.14159 \times 10^{-21}\).

Units can be typeset with \unit:

\unit{kg}

Quantities can be typeset with \qty:

\qty{3.14159}{kg}

And angles can be typeset with \ang:

\ang{90}

Writing units

The siunitx package provides a number of options for calling units. For example you can use full names or abbreviations:

\unit{kg.m.s^{-1}}

or

\unit{\kilogram\meter\per\second}

These will both produce the output \(\text{kg m s}^{-1}\).

If you use the option per-mode=symbol you will instead get the output \(\text{kg m/s}\).

Custom Units

The siunitx package also allows you to define custom units using the \DeclareSIUnit command:

\DeclareSIUnit{\lightyear}{ly}

You can then use this custom unit in the same way as the built-in units:

\qty{1}{\lightyear}

This will produce the output \(1 \text{ ly}\).

units

The units package is simpler and easier to use than the siunitx package, but it is also less powerful and flexible.

Basic Usage

To use the units package, you must first include it in your document preamble:

\usepackage{units}

Numbers can be typeset with \unit:

\unit[3.14159e-21]{kg}

This will produce the output \(3.14159\text{e}^{-21} \text{ kg}\).

Fractional units can be typeset with:

\unitfrac[3.14159]{kg}{m}

This will produce the output \(3.14159 \text{ kg/m}\).