Notes on Mac OS X is like Notes on iOS: a basic, skeuomorphic note taking app that lets you type notes, format text, and add images from either operating system, and have them sync up if you’re using iCloud. There’s nothing super tricky about the app on OS X, but the default font size might be a bit too small for you.
If you want to change the size of the text that appears when you just start typing in Notes, here’s what to do.
You’re going to have to edit a system preference file, called a plist. Head into the Finder, and then hit Command-Shift-G, or select Go To Folder… from the Go menu. This will bring up a little text field, in which you need to type or paste the following file path:
This will open up the folder that contains the configuration files for the Notes app, including the file, DefaultFonts.plist. Double click this file to open it in a text editor, and find the section, repeated for each font enabled in Notes, that says
To change the font sizes back to their previous values, simply re-edit the plist file, changing the font sizes to the original values, and save the file again.
Via: Addictive Tips