To measure a computer screen, use a tape measure. Measure the screen diagonally by placing a tape measure on the bottom right corner or bottom left corner of the screen and extend it to the opposite end. Measure just the visible part of the screen, excluding the framed part.
Next, measure both the height and width of the screen. To measure the height, place a tape measure at the bottom end of the screen and extend it vertically to the top end of the screen. To measure the width, place a tape measure on the left end of the screen and extend it horizontally to the right end of the screen.