As far as I can tell, the display is 3 cm wide and 3 cm tall. I know that the resolution of the display is 128 x 128 pixels, which must mean that one pixel is
300 mm / 128 pixels = 2.34375 mm
I tried to find specifications on the display width and height, but was unable to find that, so I had to measure the display using a measuring tape... It is POSSIBLE that the actual width of the display is not 3.00 cm, but it is very close.