Thanks for the calculations. I didn't think about calculating it like that
So I also looked at the Onyx Boox M90 (
http://www.onyx-boox.com/onyx-boox-m90/specifications) and did the numbers:
The Onyx Boox M90/M91S is 9.7" with 16:11 aspect ratio (the screen is 1200 x 825) so the screen dimensions are roughly 8" x 5.5" = 44 sq in [20.32cm x 13.97cm].
Edit: Kindle DXG: 9.7" screen with 150:103 aspect ratio (the screen is 1200 x 824) so the screen dimension are 8" x 5.49" = 43.92 sq in [20.32cm x 13.94cm]. Basically the same as the Onyx M90.
iPad: 7.76" x 5.82" = 45.16 sq [19.71cm x 14.78cm]
Galaxy Tab 10.1: 8.56" x 5.35" = 45.82 sq in. [21.74cm x 13.58cm]
Of all the 3 so far, it seems that the iPad is the widest. I wonder how that affects reading in portrait mode? Although the difference between the Galaxy Tab 10.1 and the Kindle DX/Onyx M90 is pretty negligble.