TexasCHLforum.com

Pretty exact measured dimensions in millimeters:
Ring Width Height
X 55 78
10 100 150
9 200 300
8 300 450
7 400 600

I made an 11x17 target that I use at the range because I'm cheap. You can find it at:
http://www.safezonetexas.com/images/B-2 ... target.pdf
Print it with no scaling, and you've got most of the 8 ring. The lines on the edge won't print because of the printer margins, but you get a really good idea of the size.