Big Font is a very useful app for increasing font size on your Android device. It is designed to work with Android 2.3.3 and up. The app itself is very easy to use. Download it, install it, and run it. Slide your finger to the desired percentage of font size from 100 % to 115% or even 130 %. I think its very good for people with weak sight. It’s available for free on Google Play. You can download it from here.