TeX - LaTeX Stack Exchange is a question and answer site for users of TeX, LaTeX, ConTeXt, and related typesetting systems. It only takes a minute to sign up.
Sign up to join this community
\documentclass{sig-alternate}
This previous line leads to a dimension 595 x 841 (according to pdf information).
\pdfpagewidth=8.5in
\pdfpageheight=11in
Those lines enabling another dimension, 612 × 792, which was required. Are there other possibilities to ensure 8.5x11 in?
Class sig-alternate does not set the driver dependent paper size. Therefore you get the default that is configured for pdfTeX, in your case A4. Also LaTeX's \paperwidth and \paperheight are not set (see egreg's comment).
If \paperwidth and \paperheight are set correctly, then package geometry can do the driver dependent part (e.g. setting \pdfpagewidth and \pdfpageheight for pdfTeX; \special{papersize=...,...} for dvips; …). Option pass lets the page layout settings unchanged. Option showframe displays the page layout.
\documentclass{sig-alternate}
% Set letter paper size:
\setlength{\paperheight}{11in}
\setlength{\paperwidth}{8.5in}
\usepackage[
pass,% keep layout unchanged
% showframe,% show the layout
]{geometry}
\begin{document}
\noindent Hello World
\end{document}
PDF paper size: 8.50 x 11.0 in
Result with showframe:
sig-alternateclass doesn't use\paperwidthor\paperheight, nor\pdfpagewidthand\pdfpageheight. Just set the two parameters and you're done. How the type block is placed on the page is another matter.