geometry package - paperwidth and paperheight aren't accurate

Question

recognize this simple example:

\documentclass[]{article}
\usepackage[paperwidth=612.0pt, paperheight=792.0pt]{geometry}

\begin{document}
Hello World
\end{document}

I compiled it with pdflatex. Additionally I wrote this small Java-Programm (using the iText library):

PdfReader reader = new PdfReader("example.pdf");
Rectangle psize = reader.getPageSize(1);
System.out.println(psize.getHeight());
System.out.println(psize.getWidth());

The result:

Height: 789.041
Width: 609.714

Why is the paperwidth and paperheight different to the tex?

Answer 1

Because the unit is different. 1 point for TeX is 1/72.27 in, while many other programs use a PostScript point, which is 1/72 in. This is called a big point (bp) in TeX.

See also What are the various units (ex, em, in, pt, bp, dd, pc) expressed in mm?