From the developer.android.com :
Toolbar supports a more focused feature set than ActionBar. From start
to end, a toolbar may contain a combination of the following optional
elements:A navigation button. This may be an Up arrow, navigation menu toggle,
close, collapse, done or another glyph of the app’s choosing. This
button should always be used to access other navigational destinations
within the container of the Toolbar and its signified content or
otherwise leave the current context signified by the Toolbar. The
navigation button is vertically aligned within the Toolbar’s minimum
height, if set.
So if you set minHeight attribute the same as your toolbar height (layout_height ), the back arrow will be centered vertically.