[android] Adjust icon size of Floating action button (fab)

The new floating action button should be 56dp x 56dp and the icon inside it should be 24dp x 24dp. So the space between icon and button should be 16dp.

<ImageButton
    android:id="@+id/fab_add"
    android:layout_width="56dp"
    android:layout_height="56dp"
    android:layout_gravity="bottom|right"
    android:layout_marginBottom="16dp"
    android:layout_marginRight="16dp"
    android:background="@drawable/ripple_oval"
    android:elevation="8dp"
    android:src="@drawable/ic_add_black_48dp" />

ripple_oval.xml

<ripple xmlns:android="http://schemas.android.com/apk/res/android"
    android:color="?android:colorControlHighlight">
    <item>
        <shape android:shape="oval">
            <solid android:color="?android:colorAccent" />
        </shape>
    </item>
</ripple>

And this is the result I get:

I used the icon from \material-design-icons-1.0.0\content\drawable-hdpi\ic_add_black_48dp.png
https://github.com/google/material-design-icons/releases/tag/1.0.1

How to make the size of the icon inside the button be exactly as described in guidelines ?

http://www.google.com/design/spec/components/buttons.html#buttons-floating-action-button

Make this entry in dimens

<!--Floating action button-->
<dimen name="design_fab_image_size" tools:override="true">36dp</dimen>

Here 36dp is icon size on floating point button. This will set 36dp size for all icons for floating action button.

Updates As Per Comments

If you want to set icon size to particular Floating Action Button just go with Floating action button attributes like app:fabSize="normal" and android:scaleType="center".

  <!--app:fabSize decides size of floating action button You can use normal, auto or mini as per need-->
  app:fabSize="normal" 

  <!--android:scaleType decides how the icon drawable will be scaled on Floating action button. You can use center(to show scr image as original), fitXY, centerCrop, fitCenter, fitEnd, fitStart, centerInside.-->
  android:scaleType="center"

<ImageButton
        android:background="@drawable/action_button_bg"
        android:layout_width="56dp"
        android:layout_height="56dp"
        android:padding="16dp"
        android:src="@drawable/ic_add_black_48dp"
        android:scaleType="fitXY"
        android:elevation="8dp"/>

With the background you provided it results in below button on my device (Nexus 7 2012)

Looks good to me.

You can play with the following settings of FloatingActionButton : android:scaleType and app:maxImageSize. As for me, I've got a desirable result if android:scaleType="centerInside" and app:maxImageSize="56dp".

You can use iconSize like this:

    floatingActionButton: FloatingActionButton(
      onPressed: () {
        // Add your onPressed code here
      },
      child: IconButton(
        icon: isPlaying
            ? Icon(
                Icons.pause_circle_outline,
              )
            : Icon(
                Icons.play_circle_outline,
              ),
              iconSize: 40,
              
        onPressed: () {
          setState(() {
            isPlaying = !isPlaying;
          });
        },
       
      ),
    ),

As FAB is like ImageView so You can use scaleType attribute to change the icon size likewise ImageView. Default scaleType for a FAB is fitCenter. You can use center and centerInside to make icon small and large respectively.

All values for scaleType attribute are - center, centerCrop, centerInside, fitCenter, fitEnd, fitStart, fitXY and matrix.

See https://developer.android.com/reference/android/widget/ImageView.ScaleType.html for more details.

There are three key XML attributes for custom FABs:

• app:fabSize: Either "mini" (40dp), "normal"(56dp)(default) or "auto"
• app:fabCustomSize: This will decide the overall FAB size.
• app:maxImageSize: This will decide the icon size.

Example:

app:fabCustomSize="64dp" 
app:maxImageSize="32dp"

The FAB padding (the space between the icon and the background circle, aka ripple) is calculated implicitly by:

4-edge padding = (fabCustomSize - maxImageSize) / 2.0 = 16

Note that the margins of the fab can be set by the usual android:margin xml tag properties.

What's your goal?

If set icon image size to bigger one:

1. Make sure to have a bigger image size than your target size (so you can set max image size for your icon)

2. My target icon image size is 84dp & fab size is 112dp:

   <android.support.design.widget.FloatingActionButton
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:layout_gravity="center"
       android:src= <image here>
       app:fabCustomSize="112dp"
       app:fabSize="auto"
       app:maxImageSize="84dp" />
   

Try to use app:maxImageSize="56dp" instead of the above answers after you update your support library to v28.0.0

off of @IRadha's answer in vector drawable setting android:height="_dp" and setting the scale type to android:scaleType="center" sets the drawable to whatever size was set

If you are using androidx 1.0.0 and are using a custom fab size, you will have to specify the custom size using

app:fabCustomSize="your custom size in dp"

By deafult the size is 56dp and there is another variation that is the small sized fab which is 40dp, if you are using anything you will have to specify it for the padding to be calculated correctly

The design guidelines defines two sizes and unless there is a strong reason to deviate from using either, the size can be controlled with the fabSize XML attribute of the FloatingActionButton component.

Consider specifying using either app:fabSize="normal" or app:fabSize="mini", e.g.:

<android.support.design.widget.FloatingActionButton
   android:layout_width="wrap_content"
   android:layout_height="wrap_content"
   android:src="@drawable/ic_done_white_24px"
   app:fabSize="mini" />