2048 x 1536, four times that of the current Apple iPad mini and equal to the resolution of the screen on the fourth-generation Apple iPad. Because the 7.9 inch screen on the latter is smaller than the larger Retina display tablet, the pixel density would be higher and in fact, would be 324ppi on the next-gen iPad mini.
By raising the resolution on a smaller screened device, Apple gets to offer a higher-resolution device without requiring developers to rework their apps to a new screen size. This isn't the first time that rumors of a higher resolution screen for the next generation Apple iPad mini have appeared, and this past November the same exact rumor was leaked. We have always gone with the thought that where there is smoke there is fire. To see a similar difference in pixel density, take a look at the image that accompanies this article. It shows the difference between the 132ppi pixel density on the Apple iPad 2 with the 264ppi screen on the fourth-generation iPad.
source: MyDrivers, BrightWire via AppleInsider