The ecological footprint measures human demand on nature, i.e., the quantity of nature it takes to support people or an economy. It tracks this demand through an ecological accounting system that contrasts the biologically productive area people use for their consumption to the biologically productive area available within a region or the world. In short, it is a measure of human impact on Earth’s ecosystem and reveals the dependence of the human economy on natural capital.
How Many Earths Do Americans Need? 8.4 Earths!
If everyone on Earth lived like we do here in the United States, we would need 8.4 Earths. See here for more information.
How Many Earths Do You Need?
Here is a simple online ecological footprint calculator you can use to give an idea of where you stand.