Ph.D candidates Ryan White and Bryan Gauntt of Penn State University took a very close look at the iPhone 4’s Retina Display using a microscope. They measured the sub-pixel sizes and found the ones in the iPhone 3G to be 13×40 microns. Each pixel would be about 40×40 microns including the two TFT lines among the three sub-pixels. The sub-pixels on the iPhone 4G were smaller by exactly 1/4 at 6.5×20 microns. Pixel dimensions are probably 20×20 microns. Read Retina Display and iPhone 4 for more info. Additional closeups at Engadget.