How to fit a large text on one page using scrlttr2?

Question

EDIT: During the comments I noted that I should not try to change the top margin manually to keep the DIN - therefore my question is now only how can I reduce font size without changing the right and left margin.

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I try to write a covering letter with scrlttr2. My goal is to fit my text on one page. I have found the following tricks to gain more space:

I found here that one can reduce the bottom margin with the class option:

firstfoot=false

I also found that I can reduce the top-margin with:

\LoadLetterOption{DINmtext}

I found here that I could reduce the top-margin further with

\setkomavar{fromname}{%
\vspace{-\useplength{firstheadvpos}}%
Me, I  and myself}

but it didnt work for me.

I thought as a final step I could reduce the fontsize. But whenever I reduce the fontsize, the left and right margin becomes larger. How can I change the fontsize without changing the margin, or what else can I do to gain more space for my text?

Here is my code:

\documentclass[%
    max-mustermann,
    fromlogo=false,
    enlargefirstpage,
    fontsize=12pt,
    parskip=on,
    firstfoot=false]
{scrlttr2}
\LoadLetterOption{DINmtext}
\usepackage{lmodern}
\usepackage[T1]{fontenc}
\renewcommand{\familydefault}{\sfdefault}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage{blindtext}
\setkomavar{subject}{My applicationn}
\setkomavar{backaddress}{Mr. Max,Maxstreet 5, 10715 Berlin}
\begin{document}
\begin{letter}{Musterunternehmen\\ Musterstraße 12\\
12345 Musterstadt}
\opening{Hello everyone,}
\blindtext
\blindtext
\Blindtext
\closing{Best regards,}
\end{letter}
\end{document}

Answer 1

I'm not sure you want to read this.

KOMA-Script gives you a good typographic letter with in your case german rules. For example it gives the adress the right position so that you can simply use a windowed envelope to send the letter. With option DINmtext you can't use a windowed envelope.

I can not see a relevant reason to give up this automatic.

So if you not have to use the german (or other) rules for a letter you can use each document class you want, for example follow @werner answer.

If you have to follow the rules use KOMA-Script with the usual behaving and accept to get two pages or make your text shorter, if possible.

If you insist in changing the font size (use option fontsize=10pt, I would not use a smaller one!) but using the given margins you can use package geometry, for example set right and left margin to 1 cm:

\usepackage[left=1cm,right=1cm]{geometry}

Answer 2

I would suggest avoiding a document class that restricts you such freedom. For that, set the letter using the (ordinary) article document class:

\documentclass{article}
\usepackage[margin=.5in]{geometry}
\usepackage{lmodern}
\usepackage[T1]{fontenc}
\renewcommand{\familydefault}{\sfdefault}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage{blindtext}

\setlength{\parindent}{0pt}% No paragraph indent
\pagestyle{empty}
\begin{document}

\underline{Mr.\ Max, Maxstreet 5, 10715 Berlin}

\bigskip

Musterunternehmen \\
Musterstraße 12 \\
12345 Musterstadt

\bigskip

\hfill\today

\bigskip

\textbf{My application}

\bigskip

Hello everyone,

\medskip

\blindtext
\blindtext
\Blindtext
\blindtext

\medskip

Best regards,

\bigskip

Author

\end{document}

Perhaps there are some minor differences between your output under KOMA-Script, but the modifications are fairly straight-forward and easy to manipulate. I've just made a quick mock-up, so it can form a base for what you're after.