Screen size is number of distinct pixels in each dimension that can be displayed. Two factors are most important in Screen Size that is size and resolution. The size is generally measured diagonally in inches, and the resolution is on the number of pixels displayed on the screen. The smaller screens have a portrait orientation, while the large screens have landscape orientation. Number of columns and rows of pixels is known as resolution. A display with 240 pixel columns and 320 pixel rows generally said to have a resolution of 240x320.
The common resolution is 240×320.Mostly 75% of phones provide a screen resolution of 240×320 pixels or more. 68% strictly equals to 240×320. Screen resolution is frequently referred to as a modification of the classic VGA resolution 640x480 pixels. Biggest screen size for mobile phones is 800 x 480 pixels (WVGA).
There is a lot of display resolution is available. Most of the High end smart phone having the display resolution of 1080 x 1920 pixels, the second level resolution is 800 x 1280pixels and third level resolution is 768 x 1280pixels. some of the pixel resolutions are
QVGA : quarter VGA (240x320 pixels)
HVGA : half VGA (320x480 pixels)
WVGA : wide VGA (480x800 pixels)
FWVGA : full wide VGA (480x854 pixels)
nHD : one-ninth high definition (360x640 pixels)
qHD : one-quarter high definition (540x960 pixels)
HD : Half-High Definition (720x1280 pixels)
FHD : Full High Definition (1080x1920 pixels)
QHD : Quad high definition (2560x1440 pixels)