HB Blog 126: Android For Graphic Designers.

Graphic designers aren't programmers and sometimes don't know how to properly prepare graphic assets for developers. This simple tutorial should help them to do their job better, and to simplify developers lives.

Screen densities and icon dimensions

Qualifier	DPI	Scaling factor	Launcher icon	Action bar, tab icon	Notification icon (API 11)	Notification icon (API 9)	Notification icon (older)
ldpi	120	0.75	36 x 36 32 x 32	24 x 24 18 x 18	18 x 18 16 x 16	12 x 19 12 x 12	19 x 19 16 x 16
mdpi	160	1.0	48 x 48 42 x 42	32 x 32 24 x 24	24 x 24 22 x 22	16 x 25 16 x 16	25 x 25 21 x 21
hdpi	240	1.5	72 x 72 64 x 64	48 x 48 36 x 36	36 x 36 33 x 33	24 x 38 24 x 24	38 x 38 32 x 32
xhdpi	320	2.0	96 x 96 84 x 84	64 x 64 48 x 48	48 x 48 44 x 44	32 x 50 32 x 32	50 x 50 42 x 42
xxhdpi	480	3.0	144 x 144 126 x 126	96 x 96 72 x 72	72 x 72 66 x 66	48 x 75 48 x 48	75 x 75 63 x 63

Notice: the first icon dimension in table cell is full asset size, the second icon dimension is optical square. Dimension values are in pixels.
Tip: creating ldpi assets is not really needed anymore. The devices are rare and the platform will just scale down mdpi.

Google Play asset dimensions 

Asset Type	Required	Image type	Dimension
Screenshot	yes	JPEG or 24-bit PNG (no alpha)	min length for any side: 320 px max length for any side: 3840 px
High-res app icon	yes	32-bit PNG (with alpha)	512 x 512 px
Feature graphic	yes	JPEG or 24-bit PNG (no alpha)	1024 x 500 px
Promotional graphic	no	JPEG or 24-bit PNG (no alpha)	180 x 120 px
Video link	no	URL of YouTube video	-

Dimension units

Unit	Units / physical inch	Density independent	Same physical size on every screen
px	varies	no	no
in	1	yes	yes
mm	25.4	yes	yes
pt	72	yes	yes
dp	~160	yes	no
sp	~160	yes	no

Size buckets

Type	Dimension
Handset	smaller than 600 dp
Tablet	larger than or equal 600 dp

Notice: one dp (density-independent pixel) is one pixel on a 160 DPI screen.

Views dimensions and spacing

Touchable UI components are generally laid out along 48 dp units. Spacing between each UI element is 8 dp.

Action bar height

Qualifier	Dimension
Portrait	48 dp
Landscape	40 dp
Tablet	56 dp

Text size

Type	Dimension
Micro	12 sp
Small	14 sp
Medium	18 sp
Large	22 sp

Notice: one sp (scale-independent pixel) is one pixel on a 160 DPI screen if the user's global text scale is set to 100%.

Images and themes

Nine-patch 
A Nine-patch drawable is a stretchable bitmap image, which Android will automatically resize to accommodate the contents of the view in which you have placed it as the background, e.g. nine-patch background for button, which must stretch to accommodate strings of various lengths. The rules for nine-patch image are following:

• Standard PNG image with alpha
• Filename suffix is ".9.png", e.g. "btn_login_normal.9.png"
• Image has an extra 1 pixel wide border, used to define the stretchable/static/padding areas
• Stretchable sections are indicated by 1 px wide black line(s) in the left and top part of the border
• Static sections are indicated by fully transparent or white pixels
• Padding area (optional) is indicated by 1 px wide black line in the right and bottom part of the border

Colors

Use color primarily for emphasis. Blue is the standard accent color in Android's color palette. Note that red and green may be indistinguishable to color-blind users. Primary colors are as follows:

• #33B5E5
• #AA66CC
• #99CC00
• #FFBB33
• #FF4444

• #0099CC
• #9933CC
• #669900
• #FF8800
• #CC0000

Holo themes

Android provides three system themes:

• Holo Light
• Holo Dark
• Holo Light with dark action bar

Naming conventions

Naming conventions for drawables

Asset Type	Prefix	Example
Action bar	ab_	ab_stacked.9.png
Button	btn_	btn_send_pressed.9.png
Dialog	dialog_	dialog_top.9.png
Divider	divider_	divider_horizontal.9.png
Icon	ic_	ic_star.png
Menu	menu_	menu_submenu_bg.9.png
Notification	notification_	notification_bg.9.png
Tabs	tab_	tab_pressed.9.png

File names must contain only lowercase a-z, 0-9, or _.
Drawables for the specific views (ListView, TextView, EditText, ProgressBar, CheckBox etc.) should be named like this views keeping the naming rules, e.g. drawable for CheckBox should be named "checkbox_on_bg.png".

Naming conventions for icon assets

Asset Type	Prefix	Example
Icons	ic_	ic_star.png
Launcher icons	ic_launcher	ic_launcher_calendar.png
Action bar icons	ic_menu	ic_menu_archive.png
Status bar icons	ic_stat_notify	ic_stat_notify_msg.png
Tab icons	ic_tab	ic_tab_recent.png
Dialog icons	ic_dialog	ic_dialog_info.png

Naming conventions for selector states

State	Suffix	Example
Normal	_normal	btn_order_normal.9.png
Pressed	_pressed	btn_order_pressed.9.png
Focused	_focused	btn_order_focused.9.png
Disabled	_disabled	btn_order_disabled.9.png
Selected	_selected	btn_order_selected.9.png

Organizing drawables to directories

One drawable must have the same file name for all screen densities (ldpi, mdpi, hdpi etc.) and all these files must be organized according to density into the following directories. Here's the resources directory structure for drawables:

• res
  • drawable-ldpi
  • drawable-mdpi
  • drawable-hdpi
  • drawable-xhdpi
  • drawable-xxhdpi