What does the ecological footprint not account for?
Is it an underestimate or overestimate of your true ecological footprint size?

The ecological footprint does not document our entire impact on nature. It only includes those aspects of our waste production and resource consumption that could potentially be sustainable. In other words, it shows those resources that within given limits can be regenerated and those wastes that at sufficiently low levels can be absorbed by the biosphere. For all activities that are systematically in contradiction with sustainability, however, there is no footprint, since nature cannot cope with them. There is no sustainable regenerative rate for substances such as heavy metals, persistent organic and inorganic toxins, radioactive materials, or bio-hazardous waste. For a sustainable world, their use needs to be phased out. In other words, the above footprint calculation assumes that the person being assessed engages in none of these systematically unsustainable activities, be it for example the release of CFCs, the unsafe disposal of motor oil, or the purchase, use and disposal of other harmful household chemicals.

Information Credit: This information was provided by the Ecological Footprint spreadsheet developed by Wackernagel et al (2000).