On Mobile devices the viewable image size is the actual amount of screen space that is available to display a picture, image etc. Display size is generally measured diagonally in inches. Most of the devices use 3–3.5 inch screens. Mobile screen sizes start from 1 inch and goes 4.0-inch, 4.8-inch, 4.5-inch, 4.3-inch, 5 inch respectively. The average screen size of smartphones ranges from 3.5 inches to 4.5 inches. 

Display size can be measured by the Diagonal of the screen without the frame around the screen that is the visual screen.Most of the smart phones comes with higher screen size that helps for viewing text-heavy Web pages, and reduces the trouble of scrolling. The drawback of the higher screen size is they are require more power and used most of the battery backup of the smart phone.