It is a resource management tool that measures how much land and water area a human population requires to produce the resources it consumes and to absorb its waste under prevailing technology. By measuring the ecological footprint we can assess if we have enough capacity on the planet to sustain our lives. When our ecological resource demands to grow our food, produce the products we use and eliminate our waste exceed what nature can supply, we move into what is termed ecological overshoot. The ecological footprint is a resource accounting tool used to address underlying sustainability questions. It measures the extent to which humanity is using nature’s resources faster than they can regenerate. On a global level, humanity is exceeding its ecological limits by 39%.

Additional Resources
  http://www.conservation.org/act/live_green/Pages/ecofootprint.aspx?KNC-adwords&gclid=CKDDpZGYtpQCFQqdnAod_kR6Sw

http://www.myfootprint.org/en/

http://www.footprintnetwork.org/