use the build in sizes like
Material text sizes XML for Android
Simple helper file for standard text sizes in material design. The sizes are provided by the material design documentation https://www.google.com/design/spec/style/typography.html#typography-roboto
Too many type sizes and styles at once can wreck any layout. A typographic scale is a limited set of type sizes that work well together, along with the layout grid. The basic set of styles are based on a typographic scale of 12, 14, 16, 20, and 34.