The Earth Day Network Footprint Caclculator helps you find out "how many planets it takes to support your lifestyle."
According to their website, the "Earth Day Network was founded on the premise that all people, regardless of race, gender, income, or geography, have a moral right to a healthy, sustainable environment. Our mission is to broaden and diversify the environmental movement worldwide, and to mobilize it as the most effective vehicle for promoting a healthy, sustainable environment. We pursue our mission through a combination of education, public policy, and consumer activism campaigns. Our campaign and programs are predicated on the belief that an educated, energized population will take action to secure a healthy future for itself and its children. Earth Day Network has a global reach with a network of more than 17,000 partners and organizations in 174 countries. More than 1 billion people participate in Earth Day activities, making it the largest secular civic event in the world."