How to adjust the width of abstract?

Question

I would like to change my abstract's text width. For now I have something like this:

\begin{abstract}
\lipsum
\end{abstract}

I have tried wrapping my text with

\begin{minipage}{0.85\textwidth}
...
\end{minipage}

But then : I don't know if that's the correct way + the problem is with centering this text after resizing it.

EDIT

The beginning of the document:

\documentclass[a4paper,12pt]{article}
\usepackage{times}          % Use the Times font.
\usepackage[T1]{fontenc}    % Check that ÖÄÅöäå come out ok!
\usepackage[utf8]{inputenc}
\usepackage{epsfig}         % If you embed EPS pictures.

\setlength{\parindent}{0mm} % Do not indent the 1st line of a paragraph.
\setlength{\parskip}{3mm}   % Add space between paragraphs.

% Save some paper by stuffing more text on each page:
% A4: 210mm x 297mm, approximately 35 mm margins on every side.
\addtolength{\topmargin}{-18mm}    
\addtolength{\textheight}{30mm}    
\addtolength{\oddsidemargin}{-6mm} 
\addtolength{\textwidth}{14mm}     

\begin{document}
...

Answer 1

The standard abstract environment, when the titlepage option is not given, just calls for a quotation environment.

You can redefine the environment and use a customized list environment instead.

The standard definition is equivalent to

\newenvironment{abstract}
 {\small
  \begin{center}
  \bfseries \abstractname\vspace{-.5em}\vspace{0pt}
  \end{center}
  \quotation}
 {\endquotation}

(unless the twocolumn or titlepage options are given).

For example, in order to have an indent by 5mm on each side, you can do

\renewenvironment{abstract}
 {\small
  \begin{center}
  \bfseries \abstractname\vspace{-.5em}\vspace{0pt}
  \end{center}
  \list{}{%
    \setlength{\leftmargin}{5mm}% <---------- CHANGE HERE
    \setlength{\rightmargin}{\leftmargin}%
  }%
  \item\relax}
 {\endlist}

Here's a complete example, where I also changed some of your calls.

\documentclass[a4paper,12pt]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[margin=35mm]{geometry}% <-------- CHANGE HERE for the global margins
\usepackage{mathptmx} % for Times

\usepackage{graphicx} % for embedding pictures

\usepackage{lipsum} % just for the example

%\setlength{\parindent}{0mm} % Do not indent the 1st line of a paragraph.
%\setlength{\parskip}{3mm}   % Add space between paragraphs.

\renewenvironment{abstract}
 {\small
  \begin{center}
  \bfseries \abstractname\vspace{-.5em}\vspace{0pt}
  \end{center}
  \list{}{
    \setlength{\leftmargin}{.5cm}%
    \setlength{\rightmargin}{\leftmargin}%
  }%
  \item\relax}
 {\endlist}

\begin{document}
\begin{abstract}
\lipsum*[2]
\end{abstract}
\lipsum[3]
\end{document}

You shouldn't use epsfig, but graphicx. Also geometry is better than guessing at the page shape parameters. With this setting you get 35mm at each side of the paper, change to suit. Much more customizations are possible, see the manual.

Instead of times (which is obsolete), call mathptmx. For better results with math formulas, the combination

\usepackage{newtxtext,newtxmath}

might be preferred (I recommend it, instead of mathptmx).

Please, don't do \setlength{\parindent}{0pt} and \setlength{\parskip}{3mm}; to begin with, the 3mm value is arbitrary and not tied to the font parameters. But the most important aspect is that these settings add white horizontal bands to each page that make it awful. And less legible.

Answer 2

Try the following code.

It redefines the quotation environment locally inside the abstract environment, and you can change the amount of \leftmargin, so to change the margins of the abstract.

\documentclass[a4paper,12pt]{article}
\usepackage{lipsum}

\let\oldabstract\abstract
\let\oldendabstract\endabstract
\makeatletter
\renewenvironment{abstract}
{\renewenvironment{quotation}%
               {\list{}{\addtolength{\leftmargin}{1em} % change this value to add or remove length to the the default
                        \listparindent 1.5em%
                        \itemindent    \listparindent%
                        \rightmargin   \leftmargin%
                        \parsep        \z@ \@plus\p@}%
                \item\relax}%
               {\endlist}%
\oldabstract}
{\oldendabstract}
\makeatother

\begin{document} 
\begin{abstract}
\lipsum[1]
\end{abstract}

\lipsum[1]
\end{document} 

Output