# \hspace{1pt} is equivalent to what spacing commands, in math-mode?

I'm using the command \hspace{1pt} as a small space in many maths expressions, to adjust the horizontal spacings to my taste. Frequently, the standard spacing commands \, and \: are too much, and adding a tiny space is enough. However, I don't like to define an absolute space (1pt) since I may need to change the font size (currently, I'm using 11pt standard fonts). So what would be a proper replacement to \hspace{1pt} in terms of other standard spacing commands?

Here's a silly MWE to play with, party, laugh and have fun:

\documentclass[11pt,letterpaper,twoside]{book}
\usepackage{lmodern}
\usepackage{amsmath}
\usepackage{tensor}

\newcommand*{\psp}{\hspace{1pt}} % \psp for PointSPace.

\begin{document}

Blabla:
\begin{align}
y &= (\psp x - y \psp), \\
y &= (x - y).
\end{align}

\end{document}

• you said in the text that you use 11pt but your example uses 12pt, since the values in the answer totally depend on the font size, that's rather confusing. – David Carlisle Jan 23 at 16:50
• @DavidCarlisle, sorry, I edited the MWE. This code is a modification of my various MWE files! :-) – Cham Jan 23 at 16:50
• If it's for math mode then use \mspace{2mu} (or whatever value you prefer). The mu (math unit) will scale with the font. – campa Jan 23 at 16:55
• 1em=18mu but the mu will scale according to the math style. – campa Jan 23 at 16:58
• 1.5mu is exactly half of \, – David Carlisle Jan 23 at 17:18

You are specifically looking at spacing in math. For that, a common spacing measure would be mus. With this in mind, here's an extract from TeX by Topic (section 23.6 Mathematical spacing: mu glue):

Spacing around mathematical objects is measured in mu units. A mu is 1/18th part of \fontdimen6 of the font in family 2 in the current style, the "quad" value of the symbol font.

Under the different document class defaults, 1mu therefore is equivalent to

• 10pt: 1em = 10.00002pt; 1mu = 0.55554pt
• 11pt: 1em = 10.95003pt; 1mu = 0.60832pt
• 12pt: 1em = 11.74988pt; 1mu = 0.66666pt

So, for a (roughly) 1pt space, you'd need (roughly) 2mus under any document class font option. These spaces would scale with the font size, so you could define

\newcommand*{\psp}{\hspace{.1\dimexpr1em}}


or

\newcommand*{\psp}{\mskip2mu}

• Wow! You guys rock! – Cham Jan 23 at 18:32

I would not add space at the points you indicate, so simply not adding space would be my recommendation, however if you add

\showthe\dimexpr 1em /18\relax


In the text of your document you will get

> 0.60834pt.


so 1mu math space is .6pt, a thin space, \, is a space of \thinmuskip which is 3mu in the standard (and most other) classes so 1.8pt at \normalsize. So perhaps you want \mskip2mu

• So I guess that I need to replace my 1pt with 2mu. What would you suggest as a macro, instead of my \psp in the MWE above? – Cham Jan 23 at 16:58
• @Cham I would not use anything but if you want to add it it doesn't matter what you call it. \psp, \zzz, \extrathinspace, ... – David Carlisle Jan 23 at 17:00
• I'm not talking about the name, but the macro itself. What about \newcommand*{\psp}{\mspace{2mu}} ? So this is half \, right? – Cham Jan 23 at 17:03
• @Cham 2/3 \, not half. – David Carlisle Jan 23 at 17:08
• @Cham \mspace{2mu} is probably better latex syntax but requires amsmath package, it is the same as the \mskip2mu I put in my answer. – David Carlisle Jan 23 at 17:09