My understanding of the term "carbon footprint" is that is a measure of the amount of greenhouse gases that you and your family put into the environment, measured by such data as: utility bills, whether you use cfl's, temperature and size of your house, how many miles you drive, the efficiency of your vehicle, whether you carpool, use public transportation, bike or walk to work or errands, how far you travel to work, the efficiency of your appliances, if you use a clothes dry or clothes line ...

The list is almost endless as there is a lot to pay attention to. There are a number of websites that can help you make this calculation, some more detailed than others.