Enter a couple of numbers for your display, and it will tell you the width and height, and the DPI. Simple.

	Pixels wide	Pixels high
			Guess

Diagonal (" or cm)

Display name

Name	Pixels	DPI	Diagonal	Size	Pixel Count
17"	1280x1024	96	17.0" (43.2 cm)	13.3" x 10.6" (33.7cm x 27.0cm)	1310720	Remove
20" wide	1680x1050	99	20.0" (50.8 cm)	17.0" x 10.6" (43.1cm x 26.9cm)	1764000	Remove
macbook	1280x800	115	13.1" (33.3 cm)	11.1" x 6.9" (28.2cm x 17.6cm)	1024000	Remove