New Sprite

You can create a new sprite from File > New menu (Ctrl+N or ⌘N).

Here you select the sprite:

dimension (in pixels),
its color mode, and
the default background color.

The sprite is created with a specific palette by default.

Math in Numeric Fields

Numeric fields like Width and Height can evaluate little math expressions:

$Math demo in numeric field$

New Sprite from Selection

You can create a new sprite from the active selection using Edit > New Sprite from Selection (Ctrl+Alt+N or ⌥⌘N):

SEE ALSO

Color Mode | Default Palette