Try adding the below property to your spinner item, it worked for me :
android:textSize="?attr/actionBarSize"
Hope this helps..
Edit :
Okay, I wasn't telling you about toolbar, let me show an example which might help you :
I assumed in my answer that you have a custom layout defined for spinner, if not then have a look at below code :
Define spinnerLayout.xml file in your layout resource :
<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/spinnerLayoutItems"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:textSize="?attr/actionBarSize"
android:textColor="#FF0000"
android:gravity="center"/>
Now, add this in your activity :
.....
Spinner spinner = (Spinner) findViewById(R.id.spinner); // Your spinner id in layout.
.....
ArrayAdapter<String> adapter = ArrayAdapter.createFromResource(this,
R.array.list,R.layout.spinnerLayoutItems);
spinner.setAdapter(adapter);
....
So, I was telling to set your textSize in spinner to "?attr/actionBarSize", you can set it anything, as big as you want.
I am sorry, I by mistake wrote in my previous answer : android:layout_height property, I have corrected it.
Hope this helps....