Density is a really simply app for Mac that lets designers and developers calculate dimensions for multiple screen sizes. It is by far one of the most simplest utility app I have seen for OS X, but one that’s a super handy tool for anyone who works with different screen and display sizes in their line of work.
The app is a single window that lists different screen densities along with the Width and Height values in pixels. You can enter the value in any of these text boxes and Density automatically calculates and displays the corresponding values for other densities.
You can export the values generated in the app, but I found it slightly odd that the button to do this is labeled “SAVE TXT”, but the file it generates is a Rich Text (.rtf) file. There’s also a nifty option to make the window float on top of other applications, so the values are always visible.
Density is available for $0.99 on the App Store.