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
macbook	1280x800	115	13.1" (33.3 cm)	11.1" x 6.9" (28.2cm x 17.6cm)	1024000	Remove