The 48.3 cm (19 inch) [410.9 x 257 mm] measurement refers to the size of the screen that our website sells screen protectors for. This size is commonly found in desktop computer monitors and some all-in-one computers. By providing this measurement, customers can ensure that they are purchasing the correct size screen protector for their device, which will provide protection against scratches, smudges, and other types of damage. Our website offers a range of screen protectors specifically designed for this size screen, including tempered glass, anti-glare, and privacy options.