2560x1440 is ~109 dpi when the pixels are arranged to fill a 27" monitor. (This is not considered "Retina".) 2560x1440 is ~500 dpi when the pixels are squeeze

2560x1440 is ~109 dpi when the pixels are arranged to fill a 27" monitor. (This is not considered "Retina".) 2560x1440 is ~500 dpi when the pixels are squeezed into a 6" phone display such as as Google Nexus 6/6P. The "Retina" description refers to the dpi exceeding 300 dpi and not the absolute # of pixels.