# Font size decreases instead of increasing

\documentclass[12pt]{report}
\usepackage[utf8]{inputenc}

...all the packages I need

\begin{document}

\chapter*{Abstract}
bla bla bla

\pagebreak

\input{dedication}

\chapter*{Acknowledgements}
bla bla bla

\tableofcontents

\chapter{bla bla}
\input{chapters/Introduction}

\chapter{bla bla1}
\input{chapters/Chapter1}

\chapter{bla bla 2}
\input{chapters/Chapter2}

\chapter{bla bla 3}
\input{chapters/Chapter3}

\chapter{Conclusions}
\input{chapters/Conclusion}

\appendix
\chapter{Matlab Code}
\input{chapters/Appendix}

\input{chapters/reference}

\end{document}


Strangely when I change the font size to 12pt to (for example) 18pt the font size decrease instead of increasing...any help?

Thank you very much!

LaTeX will give you a warning that the 18pt option is not used. 12pt is not an arbitrary length setting a font size it is a name of a class option, like oneside the names 10pt, 11pt and 12pt just happen to look like lengths. As the option is not known, latex acts as if there were no option, so the default 10pt is used.
• @Davide [18pt] is like [unknownname] and just makes a warning that you see in the log about "unused global option" so in that case you get the default 10pt setting. If you use the 12pt option then you get a document style based on a 12pt body text. If you want large text within the document use \Large or some such command. – David Carlisle Apr 30 '15 at 10:32
• @DavidCarlisle - should the last sentence read (and for example 11pt option sets the default font size to 1*0*.95pt)? – Arash Esbati Apr 30 '15 at 11:00