Equal left and right-hand margins

Question

I am working off a thesis template which produces a document in which the left-hand side margin is bigger than the right-side margin, i.e., the text does appear in the middle of the page. What would I need to change in the following code to have equal left and right-hand side margins:

\documentclass[a4paper,12pt,twoside]{report}
\usepackage{graphicx}
\usepackage{fancyheadings} 
\usepackage{longtable}
\usepackage{float}
\usepackage{amsmath,bm}
\usepackage{epstopdf}
\usepackage{sectsty} % Allows customizing section commands
\usepackage{tabularx,ragged2e,booktabs,caption}
\usepackage{booktabs}
\usepackage{subfig}
\usepackage{multirow}
\usepackage{amsfonts}
\usepackage{csquotes}
\usepackage{rotating}
\usepackage{array}
\usepackage{siunitx,booktabs}
\usepackage{listings}
\usepackage[skip=0.333\baselineskip]{caption}
\usepackage{caption}
\usepackage{textcomp}
\allowdisplaybreaks
\usepackage{makecell}
\usepackage{dcolumn}
\usepackage{enumerate}
\usepackage{mathtools}
\pagestyle{fancyplain}
\parskip=0cm
\voffset=-0.54cm
\hoffset=0.46cm
\oddsidemargin=0pt
\evensidemargin=0pt
\topmargin=0pt
\headheight=0.5cm
\headsep=0.5cm
\textheight=23.7cm
\textwidth=15.8cm
\setlength{\headwidth}{15.8cm}
\setlength{\parindent}{0pt}

\setlength{\parskip}{1ex plus 0.5ex minus 0.2ex}

\setlength{\parskip}{10pt}

\renewcommand{\chaptermark}[1]{\markboth{#1}{}}
\renewcommand{\bibname}{References}
\lhead[\fancyplain{}{}]{\fancyplain{\slshape \leftmark}{\slshape\leftmark}}
\rhead[\fancyplain{\slshape \leftmark}{\slshape \leftmark}]{\fancyplain{}{}}
\cfoot[\fancyplain{\thepage}{\thepage}]{\fancyplain{\thepage}{\thepage}}
\setlength{\headrulewidth}{0.4pt}
\setlength{\plainheadrulewidth}{0.4pt}
\begin{document}

Many thanks.

Answer 1

First and foremost, don't specify twoside unless you want an asymmetric layout. The default for the report document class is oneside -- don't override it.

Second, I wouldn't reinvent the wheel, so to say, in terms of setting the page layout parameters. Unless there's no other choice, don't manipulate low-level parameters such as \oddsidemargin and \evensidemargin directly. Instead, I'd use the well-documented and very widely used geometry package. See below for an application.

By the way, since the total height of a4paper is 297mm, setting \textheight to 237cm guarantees that the sum of the vertical margins (60mm) must exceed the sum of the horizontal margins (52mm). Is this intentional?

\documentclass[a4paper,12pt,oneside]{report}
\usepackage[textheight=23.7cm,
            hmargin=26mm, % 210mm-2*26mm=158mm
            top=26mm, % same as left and right margins (?)
            headheight=0.5cm,
            headsep=0.5cm,
            %includeheadfoot, % optional
            %showframe % optional
           ]{geometry}
\usepackage{fancyheadings}  % I would use 'fancyhdr'
\pagestyle{fancyplain}
\lhead[\fancyplain{}{}]{\fancyplain{\slshape \leftmark}{\slshape\leftmark}}
\rhead[\fancyplain{\slshape \leftmark}{\slshape \leftmark}]{\fancyplain{}{}}
\cfoot[\fancyplain{\thepage}{\thepage}]{\fancyplain{\thepage}{\thepage}}
\setlength{\parindent}{0pt}
\setlength{\parskip}{10pt}
%%\renewcommand{\chaptermark}[1]{\markboth{#1}{}}
\renewcommand{\bibname}{References}
\usepackage{lipsum}  % for filler text
\begin{document}
\chapter{Hello}
\section{World}
\lipsum[1-40] % generate several pages of filler text
\end{document}