Paper sizes in FPDF


I have used FPDF for our documentation, and now they found that we
need bigger sizes - some new drawings are in - I guess - A2. And FPDF
can only handle max A3.

In the file fpdf.php line 119, I have updated this:

//Page format
'junior legal'=>array(576,360));

I want to share this, but also ask- is this right?

Accoding to:

1) American sizes are easy, the number about should be 72 dpi, so 8
inches = 8 * 72 = 576.
2) new A sizes are odd - they should be twice as big, but e.g the jump
from A2 to A1 increases by 1 mm (420 to twice that = 840 mm, but it is
841 mm?!?!).
Anyway, I calculated them as = size / 25,4 * 72

Any comments anyone?