Pythagoras' Theorum m'boy.
Width squared + height squared = diagonal squared
Using this, and the height to width ratio (e.g. 16:9) you can work out the visible area.
16 squared = 256
9 squared = 81
256 + 81 = 337
square root of 337 = 18.358
37 / 18.358 = 2.015
16 x 2.015 = 32.24
9 x 2.015 = 18.14
So, there you have it.
A 37", 16:9 screen has a visible area of 32.24" x 18.14".
Hav