# How to write ceil and floor in latex?

Is there a macro in latex to write ceil(x) and floor(x) in short form? The long form

\left \lceil{x}\right \rceil


is a bit lengthy to type every time it is used.

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• Thank you, it seems I was asking questions in the wrong forum indeed! – danny Jul 7 '13 at 17:35

Using \DeclarePairedDelimiter from mathtools, you could define macros \ceil and \floor, which will scale the delimiters properly (if starred):

\documentclass{minimal}
\usepackage{mathtools}
\DeclarePairedDelimiter\ceil{\lceil}{\rceil}
\DeclarePairedDelimiter\floor{\lfloor}{\rfloor}

\begin{document}
\begin{equation*}
\floor*{\frac{x}{2}} < \frac{x}{2} < \ceil*{\frac{x}{2}}
\end{equation*}
\end{document}


Result:

• Doesn't work here. Any idea how to do it without mathtools? – David 天宇 Wong Mar 5 '15 at 1:54
• Just a question: why * when using \floor? I noticed that if the * is omitted from the command, the delimiter does not resize... but why? – Gherardo Jul 11 '15 at 7:26
• @Gherardo: Check the documentation of the mathtools package. It's just the way the \DeclarePairedDelimiter macro works — you can also make it use a specific size if you want to: \floor[\Bigg]{\frac{x}{2}}. – You Jul 11 '15 at 10:10
• As a minor side note, the inequality you used as an example is incorrect for all even numbers. – Chris Feb 18 '18 at 13:35
1. You can define your own macro via the \def command anywhere in your document. For example

\def\lc{\left\lceil}
\def\rc{\right\rceil}


and then just write \lc x \rc.

2. Or you use the \providecommand in the preamble, e.g.

\providecommand{\myceil}[1]{\left \lceil #1 \right \rceil }


to simply use \myceil{x} in your document.

3. Use an editor, like vim, that allows for defining shortcuts for quick and efficient editing.
• For 1. In LaTeX you should use \newcommand not \def. For 1. and 2. using \left...\right is not appropriate in a number of situations. – Andrew Swann May 5 '18 at 8:40

This will also work fine without using mathtools.

\newcommand{\floor}[1]{\lfloor #1 \rfloor}

• Welcome to TeX.SX! \floor and \rfloor are amsmath commands, mathtools builds on top of amsmath, so it's no wonder, this would work even without mathtools. The solution with \DeclarePairedDelimiter shows better spacing however. Perhaps you should elaborate on your answer and show some screenshot and a full example, not only fragments of code – user31729 Jun 24 '15 at 23:47
• @ChristianHupfer \lfloor and \rfloor are in core LaTeX. \floor is not defined in amsmath. The \DeclaredPairedDelimiter' is good, but in comparison to the \newcommand above it mostly provides an easy way to change the code when a different size is required. – Andrew Swann May 5 '18 at 8:44

There is no need to use mathtool here:

\newcommand{\floor}[1]{\left\lfloor #1 \right\rfloor}
\newcommand{\ceil}[1]{\left\lceil #1 \right\rceil}


is better than mathtool.

• I think this is a comment to one of the previous answers, not an answer... – CarLaTeX May 5 '18 at 8:06
• This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review – Bobyandbob May 5 '18 at 8:21
• @Bobyandbob This most certainly answers the question. It might not be a very good answer (that is certainly my belief), but there should be little doubt that this is an answer to the question asked above. – moewe May 5 '18 at 11:48
• I strongly disagree with the sentiment that the approach here is better than mathtool. The mathtool` approach allows for automatic scaling (which should be used with care, if not avoided at all, because it can give sub-par results in certain cases, see e.g. here - could not find a better example) and manual specification of fence size. – moewe May 5 '18 at 11:52