Odd-even margin

Question

I am writing a book and I need to set the odd/even margin on the binding side.

\usepackage[top=2cm, bottom=2cm, left=1cm, right=1cm, headsep=14pt]{geometry}

I need left = 2.1cm for odd pages and for even one left = 1.0cm.

I found

\oddsidemargin
\evensidemargin

but those change all four sides.

How can I set two different margins on odd/even pages?

Answer 1

You can do this with the inner and outer keys. The inner (outer) margin is the left (right) margin on odd pages and right (left) margin on even pages. Hence

\usepackage[top=2cm, bottom=2cm, outer=1cm, inner=2.1cm, headsep=14pt]{geometry}

should do what you want.

As mentioned in comments below, the twoside option must also be added, either to the documentclass or geometry. The book class has this by default, while report and article does not.

Answer 2

If you are writing a "report", then

\documentclass[12pt,twoside]{report}
\usepackage[left=2in,right=1in,top=1in,bottom=1in]{geometry}
\usepackage{lipsum}
\begin{document}
\lipsum[1-10]
\end{document}