I’ve found that most elements on your site have specific font-sizes set.
For example
.main-navigation li a (The links up the top: 10 pixels)
.entry-content p (The main font in blog posts: 14 pixels)
.widget-area .widget p, .widget-area .widget .textwidget (The sidebar text: 11 pixels)
The font on your body is 14pt, I guess this is where you changed it.
But unfortunately the other fonts everywhere else on your page are set to specific sizes. I generally wouldn’t make a website/theme this way for this exact reason. I tend to prefer to use “em” or “%” which makes the fonts relative to their parent element’s font size, and occasionally I use “rem” which makes it relative to the overall document.
However WordPress plugins and themes frequently use fixed font-sizes everywhere. This makes a decision like increasing your overall font sizes quite difficult to implement!
So firstly you’re going to have to go through your theme and anywhere it mentions “font-size” and “line-height” – change it.
Then it might still be no good because you could be using a plugin that also provides CSS, so in those situations you will have to create a new CSS style rule to override the font-size.
If you want more info on font sizes:
https://css-tricks.com/css-font-size/
Also a good tool for investigating this quickly is using Chrome’s inspector (right click on some text and choose ‘inspect’ – there you will get some clues of where the font size is coming from) If you’re using Firefox the equivalent of that is using Firebug. You might need to look into how inspector/firebug work, but I assure you it’s a handy tool to know if you run a website, and even if you don’t, sometimes you see a messed up website that you really want to read and this can help you see it properly ??
