letter paper format with latex

The default seems to be A4. Various ways to change this to letter:

Directly in the document (if converting to pdf) (not tested)
\usepackage{ifpdf}
\ifpdf
\setlength{\pdfpagewidth}{8.5in}
\setlength{\pdfpageheight}{11in}
\else
\fi

In Unix, for all documents (not tested)
sudo texconfig-sys paper letter

In Windows, for all documents
With TeXlive, we can use texlive manager (run as administrator) and choose letter for all documents, under the configuration tab.