How to change the size of menu item icon in NavigationView?

In your xml file the shortest way is there is a property in NavigationView Just add it .

app:itemIconSize="12dp"

Got Solution

Make Below entry in dimens.

<dimen name="design_navigation_icon_size">48dp</dimen>

The main thing that decide the icon's size is the dimension:navigation_icon_size, have a look at the NavigationMenuItemView class:

 public NavigationMenuItemView(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    this.mIconSize = context.getResources().getDimensionPixelSize(dimen.navigation_icon_size);
}

so, we can just overide the property in our dimens file.

For example:

<dimen name="navigation_icon_size">48dp</dimen>

add that code in the dimens file, and you can find it's size changed.

Before:

After:

You can change the size of navigationView icon by overriding design_navigation_icon_size attribute. You can put it in dimens and because you're overriding a private attribute, you need to include tools:override="true"

<dimen name="design_navigation_icon_size" tools:override="true">40dp</dimen>