Screen Dimensions Calculator. Calculates the width and height of a screen (in cm and inches) according to format and diagonal There are 72 pixels in an inch. What happens if you take an image and reduce its size by half is that the pixels will be more on each inch, and we say it's now 150 ppi (pixels per inch you see). The image is still 500 x 500 pixels. If you talk about images in pixels you don't have to mention the resolution. In a 25 in TV, the length of the screen a diagonal is 25 in. To convert inches into Centimeters multiply the inch value by 2.54 (1 inch =2.54 cms or centimeters). To make screen size in inches from centimeters, divide by 2.54. In the smartphone screen image here, the screen size is marked as 10.2 cms or 4 inches which is the measurement from the bottom left corner to the top right corner. An inch is a unit of length equal to exactly 2.54 centimeters. There are 12 inches in a foot, and 36 inches in a yard. There are 12 inches in a foot, and 36 inches in a yard. A centimeter , or centimetre, is a unit of length equal to one hundredth of a meter.