In general:
Three “default” textSize values:
- 14sp
- 18sp
- 22sp
These values are defined within the following TextAppearances:
- TextAppearance.Small
- TextAppearance.Medium
- TextAppearance.Large
More information about Typography can be found in the design guidelines
Related to your question:
If you don’t set a custom textSize or textAppearance, TextAppearance.Small will be used.
Update: Material design:
New guidelines related to font and typefaces. The standard rule of 14sp remains (body).
Examples how to set textappearances
AppCompat version:
android:textAppearance=”@style/TextAppearance.AppCompat.Body”
Lollipop and up version:
android:textAppearance=”@android:style/TextAppearance.Material.Body”