interface builder: What is font size unit?

Question

Is it in pixel? Also, does it have a one-one relationship with the font in popular image editor's font size? (such as Photoshop).

Answer 1

Font sizes are nominally specified in points, where 1 point = 1/72" inch. This is true not just in IB and Xcode, but pretty much across the board. Whenever you specify a font size in a MacOS (X or classic) application, including Photoshop, the units are points. I'd imagine that's true on Windows as well.

Bear in mind that type using the same font and size may be rendered differently on different displays, depending on the display resolution, so "1 point" may not really correspond to 1/72" on screen. Early Macs had displays that were very close to 72dpi, so they were very WYSIWYG.