Leaked schematics of the rumored next iPhone 6 suggest two screen sizes and give out some specific dimensions for both models. The schematics come from Japanese Apple-centric Mac Otakara publication. The smaller model sports a 4.7" display and has the 137 x 66 x 7 mm dimensions (the iPhone 5s is at 123.8 x 58.6 x 7.6 mm while the 5" Nexus 5 is just 137.9 mm in height). The larger, 5.7" model is said to sport 157 x 77 x 6.7 mm, which is taller than a 5.7" Samsung Galaxy Note 3 but a bit narrower and a lot thinner.
Then come two sketches of the upcoming two models but their credibility is yet to be confirmed. The sketches apparently show a 4.7" and 5.5" iPhones with rounder edges, slim waistline and single-piece volume buttons.
According to the source of the sketches the devices sport 7.1 mm thickness. On the bottom, the 3.5 mm headphone jack is located on the far left instead of the right.
Based on those sketches Martin Hajek created a couple of 3D renders. While those aren't real and could turn to be based on completely false info, they still look pretty cool.
Recently, we saw a schematic of an unrealistically wide iPhone device but it isn't connected to the ones above.