\documentclass{article}%

\usepackage{gcheck}

\usepackage[a5paper, landscape, twocolumn, twoside,
   left=2cm, hmarginratio=2:1, includemp, marginparwidth=43pt, 
   bottom=1cm, foot=20pt, includefoot, textheight=300pt, heightrounded,
   columnsep=1cm]{geometry}
\geometry{showframe,dvips}

\begin{document}

\typeout{}
\dcheck\paperwidth{597.50787pt}
\dcheck\paperheight{423.94606pt}
\dcheck\textwidth{404.14963pt}
\dcheck\textheight{298.0pt}% because of 'heightrounded'
\dcheck\oddsidemargin{38.63551pt}
\dcheck\evensidemargin{10.18275pt}
\dcheck\topmargin{-33.77667pt}
\dcheck\headheight{12.0pt}
\dcheck\headsep{25.0pt}
\dcheck\footskip{20pt}
\dcheck\marginparwidth{43.0pt}
\dcheck\marginparsep{11.0pt}
\dcheck\columnsep{28.45274pt}
\dcheck\hoffset{0pt}
\dcheck\voffset{0pt}
\ccheck\mag{1000}
\checkresults
\typeout{}

\manyfoxes\manyfoxes\manyfoxes\manyfoxes
\manyfoxes\manyfoxes\manyfoxes\manyfoxes
\end{document}
