Apple is widely expected to unveil iPhone 6 with 4.7-inch and 5.5-inch display next month, however the pixel dimensions of the bigger displays is not clear.

We’ve heard conflicting reports about the resolution. While one report claimed that iPhone 6 may feature a 1704×960 resolution with a pixel density of 416 ppi (pixels-per-inch) for the 4.7-inch display, and pixel density of 356 ppi for the 5.5-inch display; code references in iOS 8 had suggested the resolution could be 828×1472.

Prominent Apple blogger John Gruber has written a detailed post on the subject. He expects Apple to launch iPhone 6 with 4.7-inch and 5.5-inch screens as the rumors have indicated, though he clarified that he hasn’t got information from anyone “familiar with the plans.” He also predicts that the 4.7-inch iPhone 6 will likely feature a resolution of 1334 x 750 with 326 ppi (which would be the same ppi as the iPhone 5s, iPhone 5c and iPhone 5), while the 5.5-inch iPhone 6 would most likely have a resolution of 2208 x 1242 with 461 ppi.

Gruber notes that keeping the same 326 ppi for the 4.7-inch iPhone 6 would be consistent with the patterns Apple has followed in the past.

They keep reusing the same pixel densities across iOS devices. In the past, I’ve speculated that this might be a matter of economy of scale — that they just cut different size displays from the same (large) sheets of LCDs. I no longer think that’s the reason. For one thing, they stick to these same pixel densities even across devices that use entirely different displays. The iPhone 5, retina iPod Touch, and retina iPad Mini all use 326 PPI displays, but all three use different LCD display technology.

I think the explanation has more to do with the physical size of user interface elements and touch accessibility. It’s about points. User interfaces in iOS aren’t specified in display pixels, they’re specified in virtual points. 

It is highly unlikely that the larger iPhone 6 displays will feature the 1136×640 resolution currently seen in the 4-inch iPhone 5s and 5c, as it would mean 4.7-inch display would have a resolution of only 277 pixels per inch, and a 5.5-inch display would come in at only 237 pixels per inch. So the display would neither show additional content, they would also not fall within Apple’s definition of Retina display, where individual pixels are impossible to make out at normal distances.

According to Gruber, if we consider the two reasons why larger displays are desirable are, which is to show more content on the display at once, and to make the content on the display physically larger, the 4.7-inch iPhone 6 with 1334×750 resolution would make more sense.

At 4.7 inches, 1334 × 750 works perfectly as a new iPhone display, addressing problem #1, showing more content. With point dimensions of 667 × 375, this display would show 1.38 times more points than the iPhone 5. At 326 pixels-per-inch, everything on screen would remain exactly the same physical size. There would just be 38 percent more room for content.

He also doesn’t think Apple will use the same 1334 × 750 resolution for the 5.5-inch iPhone 6, as it would mean that ppi would be only 307, which would meet Apple’s definition of Retina Display, but it would be lower resolution than the current iPhone 5s and 5c. He expects the display of the new top-end model to be as good or better than the previous model in every way, which is why he thinks that the 5.5-inch iPhone 6 to feature 2208 × 1242 resolution with a pixel density of 461.

Everything works at these dimensions for a 5.5-inch display. With an increase in area of 68 percent and a scaling factor of 1.06, this display would address both reasons why someone might want a very large iPhone: it would show a lot more content, and it would render everything on screen, point-for-point, a little bit bigger. And at 461 pixels-per-inch, everything would be amazingly sharp.

Gruber explains that the 1704×960 resolution for the 4.7-inch iPhone 6, which has been cited in previous rumors, would make sense only for a new iPhone with a 4.0-inch display, but not for larger displays as it would not show any additional content compared to the iPhone 5s or 5c when measured in points.

He also points out that it is unlikely that the 4.7-inch iPhone 6 and 5.5-inch iPhone 6 will feature a resolution of 1472×828 as cited in another report, as such a resolution would render everything almost 10 percent smaller on a 4.7-inch screen, and though the resolution works for a 5.5-inch screen, it would be only 307 pixels-per-inch, which would not be good enough for a top-end model as mentioned earlier.

Apple is widely expected to unveil iPhone 6 at a media event on September 9th, followed by the launch on September 19th. iPhone 6 is expected to feature an all-new ultra thin design with narrower bezels and rounded edges. It is also expected to include Apple’s new A8 chip, more durable Touch ID fingerprint sensor, and an improved 8-megapixel camera with optical image stabilization.