The WWF (World Wildlife Fund) has a nice page to calculate your personal CO2 – footprint. The result is given as the number of earths required to satisfy your lifestyle if all people on the planet would live like you.
The methodology seems far from being exact. It is more of a marketing tool to raise environmental consciousness but it does not give you any rule of thumb regarding your personal consumption style. I had a result of 1.99 earths and I felt rather dissatisfied with the actual information given (Searching on the german web page I found a very informative glossary here).