I wonder how large my personal carbon footprint is. How do I measure this?

I think I do not waste anything, reuse what I can, read recycled books, wear some recycled clothing, not shoes though. We keep up two cars that are old, don't go traveling very far in the truck, refuse to replace but rather repair if we can. We live organically as much as possible, buy locally when we can. We go 12 miles to the recycling site every other week now that the weather is colder, and we find that we are tossing less and less in volume, leaving occasional things that are still good for others.

But, together we have 7 children. Seven children who we love dearly, who are responsible, modern people who are like we are in their principles. They have small families or no children.

In spite of how I love them all, how carefully we live, I feel some kind of "collective guilt".