Your TI Calculator screen is 95 pixels wide and 63 high if it is an 8x series. TI-89 is 100 pixels high by 160 pixels wide. In Full mode, the Graph Screen's dimensions will be the same size. In G-T mode, the graph screen is half the width of the screen. In Horiz mode, the graph screen is half the height of the screen.
|Full||95 x 63|
|Horiz||95 x 31|
|G-T||47 x 63|
|Full||160 x 100|
However, on the TI-84, the 95th row and the 63rd column cannot be used to draw on. The real width to draw on is 94 and the real height 62. Going above this number will give an error message.