How to center toolbar back button?

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.

Inside ActionBarActivity

Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
  setSupportActionBar(toolbar);
  getSupportActionBat().setTitle("Hello World"); 
  getSupportActionBar().setDisplayHomeAsUpEnabled(true);
  getSupportActionBar().setHomeButtonEnabled(true);

Layout code :

<android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="@color/primary"
        app:theme="@style/ToolbarTheme"
        app:popupTheme="@style/Theme.AppCompat"/>

And style :

 <style name="AppTheme.Base" parent="Theme.AppCompat.Light">
    <item name="colorPrimary">@color/primary</item>
    <item name="colorPrimaryDark">@color/primaryDark</item>
    <item name="android:windowNoTitle">true</item>
    <item name="android:windowActionBar">false</item>
    <item name="windowActionBar">false</item>
</style>

<style name="AppTheme" parent="AppTheme.Base">

Remember that toolbar is just viewgroup, so u can style it in any way u like. Here is image link : Toolbar sample

Hope it helps.

(2020)

In case you have a non-standard toolbar height, to center the back button nowadays (2k20) with androidx Toolbar you can just use the buttonGravity property.

This allows you to use wrap_content instead of a specific height (minHeight doesn't allow you to do so):

<androidx.appcompat.widget.Toolbar
   app:buttonGravity="center_vertical"
   android:layout_height="wrap_content"
   ... />