Floating action buttons are a special case of promoted actions. They are distinguished by a circled icon floating above the UI and have special motion behaviors, related to morphing, launching, and its transferring anchor point.
There are two sizes of floating action buttons: the default size and the mini, which should only be used to create visual continuity with other elements on the screen.
Not every screen needs a floating action button. A floating action button should represent the primary action in an application. In the screen on the left, the primary action is to touch and open images in a gallery, so no floating action button is needed. On the right, the primary action is to add files. A floating action buton is appropriate.
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Do.
Try to use only one floating action button per screen, as it is the most prominent button on the screen.
Don't.
Don't.
Don’t use floating action buttons in dialogs. Use a flat button.
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Don't.
Don’t attach a floating action button to a side drawer; it could distract a user from the task they want to accomplish. Side drawers are for navigation.
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Don’t associate floating action buttons with pulldown menus.
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Don't.
Put overflow actions in the overflow menu in toolbars, not in floating action buttons.
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Do.
Don't.
Don't.
If the hallmark of the app is adding filetypes, a floating action button can morph into related actions after it is initially touched.
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However, if a set of actions that appear after touching a floating action button are unrelated to the button and are not a natural extension of it, then the actions should probably go into an overflow menu.
Don't.
Don't.
If a floating action button morphs into a toolbar, that toolbar should contain related actions. In this example, the button lets the user select the media type to add.
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Do.
Don’t morph floating action buttons into a toolbar that contains unrelated or confusing actions.
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Don't.
A floating action button can contain a list of contacts.
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It shouldn’t contain unrelated actions.
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Make floating action buttons positive actions like Create, Favorite, Share, Navigate, and Explore.
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In general, avoid using floating action buttons for destructive actions like Archive or Trash; unspecific actions; alerts or errors; limited tasks like cutting text; or controls that should be in a toolbar, like volume control or changing a font color. Floating action buttons don’t contain app bar icons or status bar info like notifications. Don’t layer badges or other elements over a floating action button.
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Use the circle-shaped icon consistently so as not to confuse users.
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Don’t make floating action buttons bounce.
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Don't.
A floating action button can be placed according to the keyline spacing rules or attached to an extended app bar.
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A floating action button can attach to a footer or to an extended sheet.
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A floating action button shouldn’t float in a random location. Take care when attaching floating action buttons to a toolbar, where it might overlap with or cover other touch targets.
Don't.
Don't.
A floating action button can attach to an extended head.
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A floating action button can be attached to a toolbar or structural element within a sheet (as long as it’s not blocking other elements).
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A floating action button can be attached to the edge of a sheet.
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Don’t have more than one floating action button per screen.
Don't.
Don’t place floating action buttons inside a drawer or attached to a drawer.
Don't.
Don’t associate floating action buttons with every element on a screen.
Don't.
Don’t block floating action buttons with snackbars or toasts.
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Don't.